Wow, the whole set is spoiled, and it's going to make waves in every constructed format, for sure, without leading to something unfun/dominant taking over anywhere. Spoiler for this review? 10/10! Good job Wizards!
WhiteMost of these cards are terrible, as we've come to expect the past few years, but we understand that they have to focus on the limited environment right? We'll take it in stride because they throw in cards like...
Spirit of the Labyrinth -

Enchantment Creature - Spirit
Each player can't draw more than one card each turn.
3/1This isn't your usual hatebear... it has three power! Wow! This will really help aggressive decks that lose to Brainstorm/Jace/Gush/life not lose as often to those cards. Unlike all those bestow creatures, that feel pretty forced, and of which the complexity is developing really slowly ("guys, we had to wait until the second set in the block to make +X/+Y templated ones otherwise you wouldn't get it"), this is an enchantment creature with an enchantment-like static ability. Cool!
OK, that's it for white. On to the next color.
BlueIntellect Helix - 
Instant
Scry 2.
Whenever you cast a blue spell, if Intellect Helix is in your graveyard, you may return it to your hand.Boom! The future of cantrips? I think so. Holy crap is this good. Is the the card that Frantic Search was waiting for? This is kind of similar to Sensei's Divining Top, but weaker in a world where Deathrite Shaman is so dang plentiful. This is the blue Squee.
The rest of blue is pretty much instants and enchantments that grant tap abilities to creatures, so they're pretty unplayable in Vintage, and also Legacy and Modern and Standard. They're probably pretty bad in limited too, but, y'know, we'll take what we can get from a set with Intellect Helix. They can't all be winners WotC, we understand!
BlackDark Confidant -

Creature
At the beginning of your upkeep, reveal the top card of your library and put that card into your hand. You lose life equal to its converted mana cost.
2/1Yes, it's a reprint, but Wizards clearly saw that the reprinting Modern Masters didn't budge the price of Bob, so they put it in Theros block too. And with new art to evoke the Ancient Greek flavor? I really like this version, sorry Bob Maher! It's still a Mythic, but in a set with larger print run than Modern Masters, and anyway I'm just glad they didn't try to make this card work with the
Inspired mechanic instead. That probably would have led to a hyped up card that would just make those who can't afford Bob feel like second-class citizens in a couple of years. No one wants that, right WotC? Thanks for giving us a third shot at cracking Dark Confidants in our packs, seeing one of the best designed cards again so soon? It's pretty clear you guys are pushing Modern as a format for everyone to enjoy!
RedThe Madis King - R
Legendary Creature - Goblin
R: Target noncreature artifact's controller may exile it, if he or she does, put a colorless artifact token named Gold onto the battlefield. It has "Sacrifice this artifact: Add one mana of any color to your mana pool, or add a loyalty counter to target planeswalker you control." If he or she does not, you gain control of the targeted artifact.
Don't go working yourself into a frenzy, destroying all your nice things!
1/1Gorilla Shaman, you had a good run. With how drastically WotC has pushed creatures the past five+ years, it's surprising you weren't replaced long before now. But dang, now that you have? This play on the King Midas of myth is probably going to stick around for a while. And really, it plays very differently from Gorilla Shaman. Obviously with a lot of use against Shops, this guy is good against Time Vault too. Sadly the 'noncreature' restriction is there, so Blightsteel is safe from king Midas, oh well, no card is perfect.
Shops doesn't mind giving you their Spheres, but what about their Tangle Wires and Smokestacks? Huh.... Will we see a heavier reliance on Artifact Creatures in shops to combat Midas? Revoker and Steel Hellkite, working side by side? It's been unusual before now.
Also, with the new Legend rule, Midas might be mostly battling himself back and forth... I can't imagine any player wouldn't want more gold!
GreenNyxborn Dryad -

Enchantment Creature
Indestructible.
Whenever you declare one or more creatures as attackers, you may destroy target artifact or enchantment the defending player controls.
2/1WHOA. Everything is a Trygon. This is how you compete with Tarmogoyf: indestructibility and utility. You can leave this guy back to hold off Bob indefinitely while your Insectile Aberation is impersonating (im-beast-onating? I'm gonna stay away from trying to get that right) Trygon Predator. I like that you just get one trigger (unless you have multiple Dryad's out), so that it's not overwhelmingly oppressive. This will definitely shake up Vintage, and give a boost to the BOM winning BUG deck style.
The rest of green is a bunch of 1/1's with trample and cards that give the opponent choices, so it's probably best not to dive too much deeper, we might get something on us. Ick.
MulticolorKiora, the Crashing Wave -

Planeswalker — Kiora
You may redirect combat damage dealt to Kiora to yourself.
0: Draw a card. You may play an additional land this turn.
-6: You get an emblem with "At the beginning of combat on your turn, put a 9/9 blue Kraken creature token with haste onto the battlefield."
4Kiora is really interesting, though I admit that's mostly for EDH which I love, rather than Vintage. The static ability is pretty cool, and is nice in EDH where you have more lifepoints to expend protecting her. The 0 cost ability Explore is what she's going to be doing every turn, which is a touch repetitive, but certainly powerful. We've all traded life for cards with Necropotence and Bob etc, will we do it in exchange for an Explore every turn? And most interestingly, she needs help to achieve her ultimate. Some sort of proliferate or counter transfer from old sets will interact well, along with the new 'Gold' token mechanic. This probably won't crack into Vintage play, but it's an EDH all-star.
Phenax, God of Deception -

Legendary Enchantment Creature - God
Indestructible.
As long as your devotion to blue and black is less than seven, Phenax isn't a creature.
If a card would be put into an opponent's graveyard from anywhere, exile it instead.
3/6Leyline of the Void, old friend, you look different... somehow... have you been working out? OK, smallest of the gods, but with a tried and true ability borrowed from Leyline of the Void, Phenax will be playable in Vintage, Legacy and Modern. The trifecta! Imagine that dredge kills your Turn 0 Leyline with Wispmare, and you just untap into this? Indestructible makes another great appearance here, forcing dredge to find Chain of Vapor in order to interact. How often will Phenax actually become a creature I wonder? Jace, Vendilion Clique, Confidant... that's enough to start laying the indestructible beats.
So there's a highly playable card in each color, along with a return to the way we all know Magic should be: the blue-black god is the best in Vintage. Ever since Ashiok, Liliana and Jace teamed up to make a run at the Vintage World Championships late last year we've known that WotC is doing their best to push the

color combination in Vintage away from being a list of powerful restricted cards with no equal in the other colors. I think we really have to credit WotC with making impactful cards that are well suited to Vintage without overpowering the other formats. This set gets a 10/10 from me!