Watcher in the Mist - 5 mana 3/4 flyer with Surveil 2 isn't all that constructed playable, but a fine card for limited.
Creeping Chill - 3B for a drain life for 3 isn't great nor is it bad. Surveiling it into the graveyard and doing it for free sounds entertaining to say the least.
Surveil has turned out to be the best mechanic out of this set IMO...hands down. I'd love to see the last 1/2 of this set come out and prove me wrong, but those cards would have to be totally busted.
Enhanced surveillance actually makes it better! Damn you could dig away through your deck in no time with that. With the spybug and the 1-drop wall, you can probably make a funky playable deck around surveil.
Dimir looks to be the most standard playable, izzet and boros look a little Johnny ATM. Golgari looks decent, but needs some pieces still to top dimir. Selesnya looks like mostly jank imo.
I just saw spybug...wow, Dimir is looking quite good overall and by far the best Guild in the set, at least at this point in time.
Izzet still needs some pieces but is if they have some good jump-start cards not yet revealed then it could be a contender. Boros is looking very aggressive, though countered by Selesnya (which otherwise isn't looking too good). Other that the lich and Assassin's Trophy I am not too excited about straight Golgari yet.
Enhanced Surveillance is pretty busted. Not sure if it takes Search for Azcanta's spot in a deck, but it might. Very strong abilities.
Disinformation Campaign looks like a card you might SB in. Repeatable discard effects are pretty spicy, though non-targeted pretty much means it won't see much play.
Lotleth Giant- Probably the best payoff card we have from Golgari right now. Could be the top-end finisher for a Golgari deck, but I'm not sold on that.
Ledev Guardian - a 2/4 Knight for 3W, even with Convoke, is a bad deal. It seems WotC added mana to Convoke spells and kept Surveil spells pretty much the same cost as they normally would be.
Loxodon Restorer - This card pretty much looks like the last card, Ledev Guardian. A 3/4 for 4WW with Convoke is just bad, even with the 4 life tacked on. Especially compared to the much more playable Knight of Autumn which gives you choices with its CiP effect.
Piston-Fist Cyclops - 3 mana for a 4/3 wall would be bad, but the ability to attack by casting instants/sorceries makes this at least a decent card. Still not great though.