Right, we have about 100 of the cards spoiled (including the basic lands) however as the most powerful and interesting cards are spoiled in greater abundance at the start and so this should be about half way enough to throw this out there.
Fencing Ace - B cube
As cheap doublestrike guys go this is about as good as you can hope for without it becoming insane. It has the right creature types, is easy to cast and a reasonable deal for the mana when you don't have pump effects to abuse. Most of the white two drops are either specific or WW cost while this is quite a generic bulking card that may well see play.
Jace, Architect of Thought - B cube
The worst thing about this card is that I will no longer be able to short hand refer to Mind Sculptor as 4 mana Jace. This is a very uninspiring planeswalker with effectively no abilities that permanently affect the board, a slow rate of growth and a low power ultimate. Being designed for multiplayer it is always going to be less powerful in 1v1 formats and so I cannot imagine this Jace ever being choice over any of the others for a cube deck. Having said that it isn't unplayable and is quite interesting as walkers go with lots of choices and different effects to the other more playable cards.
Grim Roustabout - C cube
Neat card and neat design but too low power to really make the cut.
Desecration Demon - 2.5
While I'm always reluctant to highly rate cards which give too much choice to your opponents, especially after Vexing Devil which has still yet to impress, this bad boy I am quite keen on. He is worse than Abyssal Persecutor as he effectively has no evasion and is a very unreliable blocker as well and so probably won't see too much play in control decks (unless some ones with situational mass removal such as Infest and Earthquake are viable that enable you to clear a board and use your Demon which survives). It is however very brutal on the offensive and not having to have ways to get rid of it yourself makes it much easier to include in decks meaning this will crop up frequently in black agro. Certainly giving your opponent choices over your cards is bad but killings guys or killing them are both good things to be doing and in many ways exactly what the fattest threat on the board with no relevant evasion does!
Pack Rats - B cube
Another cute card that would actually be pretty good in a rat deck and might also be just the ticket in a deck wanting discard outlets that also had a reasonable rat count. I think it is a little too resource intensive, slow and vulnerable to be a viable card in its own right i.e. not good in a given deck with no other rats. That being said, apart from its horrific vulnerability to Maelstrom Pulse and Echoing Truth it is a fairly serious late game threat than turns all your other dud draws into threats as well. As soon as you have invested some mana and cards into it the Pack starts to look a bit better value even without other rat support. 5 mana for 2 2/2s, 8 mana for 3 3/3s and 11 mana for 4/4s the Rats quickly become more of a bargain. I shall play around with this because I like it rather than thinking it is good enough but would like to be surprised by it and keep it in the A cube.
Underworld Connection - C cube
This is hugely worse than Phyrexian Arena which is quicker to get online, cheaper on an ongoing basis and far less vulnerable. The Connection has only two perks over it, that being optional usage which is very minor, and the potential to abuse it with untap land effects which seems overly convoluted given the low power of the card. Being able to draw the turn you make it is also not really an advantage over Arena as that would already be in play unless a late game top deck. There is too much land destruction in the cube for me to ever risk playing this. It gets its lowly slot for the potential to seriously abuse with Mind Over Matter or maybe even Earthcraft.
Guttersnipe - C cube
A quirky little storm style finisher and quite obnoxious in a burn heavy red deck but a bit too much mana for what you get on the board. If you are curving out you are unlikely to get to proc him before they have a chance to kill it and even if they don't there is a good chance it will die soon after arrival as the game unfolds and yield only one or two procs which is ok but not reliable or exciting. A storm deck would just prefer a cheaper card that was harder to remove like an enchantment and a burn deck would rather be more direct, more reliable or much quicker. Zo-Zu, the Punisher is a much more effective card for a RDW player and a spell with storm is going to be more effective for the combo player.
Mizzium Mortars - 2.0
I rather like this card as I tend to like any card that can smooth your curve by having variable costs. Burn that must hit guys is not as weak as it used to be with almost every deck containing creatures now. The card is obviously only a control as a result and so the sorcery speed is also a little tedious, particularly on the cheap end of the card. Four damage for 1R however is not to be sniffed at and will get most things dead for a low price, which is actually more important to control than being instant. Then we move onto the overload end of the card that is a one sided wrath effect which is again not unreasonably costed but wouldn't quite make the cut if it were not for the alternate. This is certainly no Bonfire of the Damned but it is a decent backup for it. You cannot make it kill things solo with five or more toughness and you cannot sneak it out as an instant but it is a cheaper and easier way of dealing three or four damage to their guys than Bonfire for the most part. One sided mass removal is one of those types of effect which will always raise an eyebrow and perk an interest and this is no let down.
Street Spasm - C Cube
I really like this card as well as the Mortars as they are very similar types of cards. This being instant made me want it to be better but sadly it is too expensive and too restrictive. When you are using an X spell to kill a creature it is rarely mana efficient and so it is not good early removal. Later on in the game you really don't want to be lumbered with removal that can't hit fliers. The non-overload portion of this card is vastly worse than the Mortars and the overload isn't much better. For the same mana cost as mass removal you get to do half the damage as Mortars and hit less creatures with it. I am not going to rule the card out and may be being overly harsh on it as one sided mass removal and dual cost cards are both very interesting.
Worldspine Wurm - 3.0
This is an Emrakul style stupid card begging to be abused with cards like Sneak Attack and Flash while also being happily powerful enough to play with Natural Order and Show and Tell. As if that wasn't enough tedious ways to end games quickly with this dork he only costs eleven mana! The 15 of Emrakul was a stretch and required good luck and a dedicated deck to actually cast however 11, particularly in green, is realistic making this altogether quite a frightening card. This has to jump right into the top 3 in the list of big fat fatties and should see a great deal of play despite not working with the reanimate strategies.
Deadbridge Goliath - B cube
This is very good but I don't see all that much in the way of a place for it in the cube. He is very fat for his cost but offers very little else. The scavenge is easy to disrupt and expensive to do and is only really the sort of thing you want to do when you are otherwise out of gas. I will certainly throw it in the cube when I get one to give it a chance to prove itself but pure cheap fat beaters need to be really good and generally also have a role, both of which are in question for this guy.
Axebane Guardian - C cube
Ramp for three mana has to be really good, generally offering card advantage or large ramping. This is too vulnerable, slow and needy of other cards to become really powerful. The only light of hope for this card is the redundancy it offers Overgrown Battlement but I can't really see a defender themed deck any time soon.
Gatecreeper Vine - C cube
Generally Sylvan Ranger is going to be the choice card in this role which is not a role that is often called upon in cube play. If the unlikely defender themed deck comes to be then this might be filler in it or if a really powerful gateway is printed it also might get some action.
Abrupt Decay 3.0
I am a big fan of this card and think it will see a good amount of play. Many people may jump to compare it to Maelstrom Pulse and Putrify however I see it in a different role. Three mana is a world of difference from two mana, particularly on a removal spell. I generally separate removal into two broad kinds, those coverall insurance removal spells that offer you a guaranteed out to a card you particularly fear and then the more situational but highly cost efficient removal cards that gain you tempo. While not as clear cut the generalisation I am about to make it is certainly a trend and that is the first kind is more control based and the latter is more agro based. This card is not a coverall insurance card in anyway as it fails to deal with all of the most serious problems however it is cheap, instant and has a very wide scope making it highly playable. The limitations on converted mana cost are compensated well by the variable targets you can hit. Control decks will still probably look to play it on top of more reliable removal as it is unlikely to be dead and sits at a great place on the mana curve. Uncounterable is a nice little tagged on bonus that won't be irrelevant either. Agro decks however will almost always play this if it is convenient colourwise as is cheap enough to offer great tempo and will serve as an out to many annoyances that will be coming out early which is when they need to be most adaptable.
Azorius Charm - B Cube
The weakest of the three charms released so far (Izzet and Selesnia) by quite some distance but still quite playable. With the high quality of cheap white and blue utility, removal and disruption cards I can't see this often making decks but it is still quite a lot of card and so will be tested out in the A cube before condemned to less glamorous life. The removal is the best aspect of the Charm but for very similar effects you can find cheaper alternatives. The lifelink is very situational and unlikely to be of much use in the decks playing it but is still a bit of life gain which is always nice to have some access too and shouldn't be fully disregarded. The card draw is effectively cycling and not at a value costing either. While it may be a low power effect compared to what is on the other charms cycling is never a dead ability and does improve the card but as such it has to be seen as a removal spell with some added situational utility rather than a card with many similarly useful effects like the other charms and commands. As gold removal this does not make the A grade for quality.
This is a bit of a game changer and could go so far as to make URB or Grixis or whatever you want to call it control decks the best of the counter based control. Typically control are weakest against planeswalkers as they have few aggressive dorks to aid in killing them. Unless they counter the walker it can be game over but now we have Dreadbore to deal with pesky walkers and everything feels a lot more relaxed on the control side of things. Certainly black already had Vampire Hexmage but it is double black as well as having a less control friendly "secondary effect". Dreadbore is a sorcery speed Terminate when it is not killing planeswalkers and this is more than acceptable a backup plan. Almost every deck will have targets for this reliable, safe and broad removal spell. BR has always been the weakest colour combination in the cube and generally only find themselves paired as a splash with many other colours involved as well. Dreadbore is exactly the kind of card that will put BR back on the map.
Dreg Mangler 3.0
Comparable to Boggart Ram-Gang most obviously for its 3/3 for 3 with haste bits. I would put them on similar levels as they are both mostly about the 3/3 for three with haste but I think the edge has to go to Mangler as a more playable card. The Ram-Gang is an odd hybrid card in that it is not always more playable than a gold card unlike most of the other good hybrids which are vastly more playable than even mono cards. As it is tripple red or green it can only go in mono red, mono green or RG which is less decks than the Dreg Mangler which is far easier to play in three colours. A 3/3 for 3 with haste is a great tempo swing and a reasonably serious threat. Add some late game flashback style value to this already appealing package and you have a pretty nice looking card. This is not the sort of dork you actively want to get in your bin as +3/+3 for 5 isn't a winning deal, it is all about applying good pressure with the attractive monster bit of the card. I am fored to give this a rating of 3 as I think its better than Ram-Gang which for some reason I have rated very highly for a restrictive gold card. With some more time to reflect on this matter I would give this a 2.5 and Ram-Gang somewhere between that and 2.0.
Corpsejack Menace - B cube
If this was a 2/2 for 2 rather than a 4/4 for 4 it would see a lot more play. The body is fine for the mana but nothing to write home about and so this card will only be used to power up other cards. Normally this would be a C cuber however there are just so many counter effects floating around at present I think this will occasionally be called upon. Lots of cards and mechanics from this set seem to work with it as well as Carrion Feeder, Phantom Centaur, undying, graft, modular and likely many more than are not springing to mind. While a bit convoluted and wishful the end result with some of these synergies is rather impressive. Fun but not good is the short conclusion for this guy.
Goblin Electromancer - 2.0
I love cards like this and will probably both vastly overrate and overplay this little fellow. Like the Guttersnipe this would be better as an enchantment or artifact simply to avoid easily being removed but that is only for the dedicated combo decks. I suspect both agro and control will be happy enough with a 2/2 dorks to apply pressure or clog up the ground that also cheapens all your spells. When the mana reduction is just a nice bonus and not an integral part of your plan it is fine to throw down unprotected and eat a removal spell or not, either way it will be good. I think it will be playable in most deck types provided they have enough cards that will be affected by it, lots of decks that are artifact heavy often have deceptively few instants and sorceries and some beatdown decks while having just enough instants and sorceries might find that too many of them have no colourless mana requirements in the cost. Around 8 cards in a 40 card deck that will be reduced by elctromancer would make it playable in most UR decks I think.
Grisly Salvage - C cube
A spell plenty powerful enough for the cube but as a gold card I can't imagine it seeing enough play. It will miss very rarely and sort you out well in the early turns but is ultimately just filler. The card quality aspect of it is good as black and green are not overdone with it but as it is an effect you don't want to load up on the existence of Demonic Tutor and Sylvan Library ensure it won't be an A cube mainstay.
Havoc Festival - C cube
The bigger version of Sulphuric Vortex is too much mana to be good as well as being a cumbersome gold card. It is powerful and could be built around with things like Academy Rector but in reality such strategies will be weak and fragile.
Hypersonic Dragon - C cube
Good but not quite there, a 4/4 flying for haste is not far off being powerful enough in its own right but is let down by being gold and having a marginal ability that would be better suited to being on a two drop.
Isperia, Supreme Judge - No slot
I feel like this should never see play over Consecrated Sphinx with it being more vulnerable, harder to cast and far less effective at gaining card advantage, especially given your opponent largely has the choice as to whether they gift you cards.
Izzet Charm 3.5
This card was a bit of a jaw dropped when I first saw it but in part that was the realisation there would ultimately be a cycle of 10 of these which is quite exciting. As all round neat little spells go this is about the best you could hope for, digging, removal and counter magic. It is really close to Fire/Ice in power and is only really let down on that front by the casting cost being a bit more demanding. Spell Pierce, Shock and Careful Study are all very playable cards in their own right and while they may cost just one mana compared to the two for Charm that is well worth it due to the broadness of the card, often those cards will be dead or poor draws while Charm will basically never find itself without a good use. The fact that the burn cannot hit players would be ruinous if it were just a burn card however with the other uses it barely matters at all. I cannot imagine counter burn decks will be built excluding this card and many more archetypes will throw in this spell too. It may even see play specifically for the Careful Study Portion as it is such a cheap and painless way to include that effect.
Jarad, Golgari Lich Lord - C cube
All just a bit fiddly and demanding to make the cut. He gets better as the game goes on but can't be relied on to be good early and requires a very specific deck - probably only black and green with a heavy creature count.
Lotleth Troll 3.5
Wild Mongrel got pumped full of steroids and came back looking highly unfair. This is well up there with the very best two drop monsters in terms of board position or aggression. He is so hard to kill with cheap regenerate, being black and having a free pitch pump effect for which you opponent is unlikely to know exactly how much it can be grown by at any given time. This hidden information aspect is quite hard to play against and is the sort of thing that you lose to when you try and Earthquake to clear the board and they just ditch their hand and go all in on the Troll. Trample is fairly minor while the Troll is still small but by four or even three power it starts to become quite annoying on a dork that can fearlessly swing every turn due to regeneration. It is the kind of card you want to play with synergic spells such as Squee, Basking Rootwalla and Gravecrawler so that you can more comfortably make use of the pump which is the best aspect of the Troll. This makes it slightly narrower in application but is powerful enough for that not to harm his cube potential.
Loxodon Smiter - C cube
Looks good but is deceptive, the two good points of this card are at odds with each other. A free cast if forced to discard makes the fact it is cheap to cast normally for its size irrelevant and vice versa. As such, if you are using it for the pitch cast it is way way worse than Obstinate Baloth or Wilt-Leaf Liege and if you are using it for a cheap powerful dork Tarmogoyf or Knight of the Reliquary are far better with many other options also appealing more from those colours. Uncounterable is not an exciting effect on a dork with no other abilities you might want to force through.
Lyev Skynight - B cube
Neat but likely just not powerful enough. I will trial this in the A cube and suspect if you could detain lands it would become a mainstay. As it stands it is a vulnerable 3 mana investment with limited added value and awkward colour requirements. Flying is nice but for three mana in white or blue better options are widely available.
Niv-Mizzet, Dracogenius - B cube
I cannot argue that this is not a lot of monster with two powerful effects. He also takes a massive poo on his previous incarnation (which I never entertained adding to my cube). I am disinclined to put vague cards in the cube that will see little play based on being gold. I call this vague because if you wanted card draw you have the vastly superior Consecrated Sphinx at your disposal and if you wanted removal on your six mana threat you have Inferno Titan, both of which are vastly better than Niv at their specific thing. Niv however does both effects even if they are a little weaker than the others. He is just the kind of durdley threat that you flop down in any draft in which you have the colours as an occasional free win blagger. He is not something you put in your carefully designed synergic deck.
Rakdos Return - No slot
Firstly Blightening is a way more cost effective way of doing this sort of thing and secondly these effects are not all that synergic. On Blightening, as with Lightening Helix it is all just about the added value on a card that is already on or above the curve for the primary effect. Whatever way you look at Rakdos Return (either a burn spell or a discard spell) it is below the curve and as such is just way to expensive and clunky to ever see play.
Selesnya Charm 3.0
The effects of this charm are more powerful than those on the Izzet Charm however they are less cohesive. There are fewer decks in which this is exactly what you want than for Izzet Charm which is the control package. The pump is good but will mostly be useful for decks applying pressure and tempo with creatures. It is not quite as narrow as the lifelink from Azorious Charm but is similar and will be less useful the more control your deck is. The removal is again the best bit of the card for which exiling a high power monster for two mana is quite a bargain. Reprisal is a great card but certainly always used to be a bit too dead in too many matchups (that might be changing these days as I have not tested it for ages) and while this is slightly worse than Reprisal in a couple of ways the fact that it cannot be dead is huge and makes it far better assuming you are in the appropriate colours. Making a 2/2 with vigilance is very generic however it is why your card is never dead and can be quite tricksy due to the instant speed. Compared to the draw a card on Azorious Charm it is far better value and more proactive. Overall a very comparable Charm to the Azorious one but with better versions of each effect and a better match for the kinds of decks using those colours.
Supreme Verdict - C cube
In cube the uncounterable aspect of this card is so rarely relevant it will not be worth the extra coloured mana, particularly with it being in another colour. I can see this card being very good in some formats but my cube isn't one of those.
Trotsani, Selesnya's Voice - C Cube
Quite a lot of card but an awkward cost both being a four drop and being white and green. Too slow, un-threatening and demanding to see much if any play. Populate being a new mechanic it will get to sit in the C cube collecting dust just in case...
Vraska the Unseen - 2.5
I first looked at this and thought it looked a lot like Gideon Jura however having played a tiny bit with one it actually felt a lot more like having an Acidic Slime. The problem is that charging her isn't an exciting effect at all as it does very little to the board state and gives your opponent all the choices. It is a well designed walker in that is is good enough to be playable but not so much so that you will almost always divert resources to killing as soon as possible. Most of the time you flop it down and deal with something scary after which it is easily killed or left to sit around doing little for you. In that respect she is most like 5 mana Chandra or even Karn Liberated. She will see more play than Chandra as she deals with more than just creatures but is certainly not an auto include in BG decks. Killing planeswalkers is the most exciting aspect of this card as it is such a rare effect and so this will be highly appealing to control decks and far less so for agro ones.
Wayfaring Temple - C cube
Interesting card but having the populate ability without any token generation makes this card not good enough. It could only be played in hardcore token decks and is therefore too narrow for the A cube.
Slitherhead - B Cube
A very neat little card that has some very nice interactions and works well as a support card in a selection of strategies. The problem is that it is very weak on its own and suffers from an incredibly low power level. When you draw it late it is underwhelming and when you make it on turn one it does basically nothing. It is like Young Wolf, a really cool card I desperately want to be playable and will search hard for places to include it but ultimately will have to accept it is just to insignificant to see much play.
Dryad Militant - 2.5
It is kind of hard to assess this card as it does nothing beyond begin a Savannah Lions in terms of synergy for your deck. How good it will be depends on how effective the ability is at disrupting your opponent which of course will be very matchup dependant. Obviously printed as a Snapcaster calmer it does help out just as well with that in cube, additionally it will harm various other recursion cards and flashback cards. I quite like the style in which it hoses graveyard effects as it allows your opponent some choice on what they need to cast and so forth where as cards like Scavenging Ooze just arrive out of nowhere and ruin everything right there and then. Suffice it to say the ability is rarely going to be bad for you while it may force suboptimal plays from your opponent. A nice mild effect taming some of the more abusable effects in cube while also being a very efficient one drop. The hybrid mana is just another perk making it more playable in a wider array of archetypes and more castable in those which are both white and green. Mostly this gets its rating for being a 2/1 for one, a bit more for being widely playable and then a final pinch of rating for an interesting disruption effect. Dryad is a weak creature type but soldier has its uses and will likely have this seeing play over the afore mentioned Savannah Lions more often than not.
Judges Familiar 2.0
A significant upgrade on Cursecatcher who has always been a little underwhelming in cube. This trades occasionally relevant creature types for basically irrelevant ones to gain flying and the ability to be cast by a second colour over Cursecatcher. I actually think this will appeal to white mages more than blue ones on the whole where the one power is less weak due to high pump and equip counts in the archetypes. Flying is also of great value in white as it is one of the few ways the archetype can obtain reach. A neat little card that won't rock worlds but will be fantastic padding for lots of decks.
Nivmagus Elemental 1.5
I am really struggling to assess this card as it is such a new style of effect. It allows for some really interesting trickery such as casting Armageddon so that your opponent sacrifices all their land to Zuran Orb to which you then eat your own Armageddon and keep your lands. This sort of trickery will be easy to pull off for a couple of months while people get used to the new mechanics but will ultimately just be another on the board trick that doesn't fool anyone. A 1/2 for an easy to play one mana is good value but isn't doing enough without eating spells as well. As such I am unsure where this will fit in, perhaps in decks like red deck wins where your late monsters and weaker spells like Larva Dart can be converted into making this guy fat. It is a bit risky investing too much in growing this guy in case he is bounced or killed and so most of the time he will wind up as a 3/4 or 5/6. The best thing about this guy is the threat he poses in combat or against damage effects as you cannot reliably block him or burn him unless you have complete information. I was originally going to stick this in the B cube but the more I look at it the more it seems really dangerous if you can afford the first spell to exile. In cube with Moxes floating around and a high number of cheap spells, many of which become weak as the game goes on or are situational, there is a lot of potential to have this guy work very well in decks. Much as I quite like the idea of using him in a storm style deck I think that is very poor, replicate on the other hand seems like it would have real potential with Mr Nivmagus.
Rakdos Shred-Freak - C cube
Flexible to cast and decent tempo but low power levels and on the vulnerable side.
Cromatic Lantern - C cube
This is almost always worse than Coalition Relic and although slightly better fixing than the two mana alternatives it is 50% more mana and not ever close to 50% more effective. I seriously doubt this will ever be used for any thing in cube play.
The Guildgates - C cube
Nothing printed so far that makes these at all interesting however worth keeping a set of aside just in case. As dual lands go they are not awful at least.