I have somewhat different evaluations than corsiKa does, so I feel like I should run down the list myself. To my mind Simic will play very much as classic blue/green tempo decks like the old Madness decks did, with undercosted midrange creatures (rather than weenies per se) and especially at the prerelease, generous amounts of card draw (as facilitated by Fathom Seer). Here are the cards I feel are particularly noteworthy, either because I think they're excellent or disagree with corsiKa:
Adaptive Snapjaw: don't sell this one short. 6/2 is awkward but means it'll trigger everyone else's evolve... but if you can get it to 8/4 this will almost always be a 2-for-1. I'm not sure what to make of it yet, but I'm curious. Also excellent, of course, for getting the 4th +1/+1 counter on your Cloudfin Raptor.
Clinging Anemones: 4 toughness means that this is a surprisingly effective Evolve enabler and not just as an evolve guy itself; it's great for Snapjaw of course, but especially for...
Cloudfin Raptor: one of the best common creatures in the set. A terrible late draw and surprisingly awkward in multiples, but any time you get to pay one mana for what can easily be a 3/4 flyer in the midgame you have to consider it a bargain.
Drakewing Krasis: awkward against opposing Crocanuras, of course, but 3-power flyers for 3 are always strong picks. This is another guy I'll take and play very highly; I expect a lot of games to end via these guys coming through the air while a Crocanura holds the ground. Handy for being a high-power guy in a world of high-toughness, low-power evolve guys.
Forced Adaptation: unlike corsiKa, I'll be sad if this ever makes my deck; not only is the 2-for-1 potential real, but it's almost never going to be any faster than just playing out another guy. Maybe if there were dense ground stalls (think Selesnya-on-Selesnya) this would be a better card, but with the sheer volumes of evasion (and pseudo-evasion like Extort), this really doesn't feel like a ground-stall set to me. My first guess is honestly something closer to Zendikar than to RTR.
Frilled Oculus: don't sell this short. At first I thought it was 1G for +2/-2 and I might still play it occasionally then. As a 2-mana 1/3 that always has the potential to go 3/5, it's a surprisingly good attacker and will do an excellent job of holding the ground.
Ivy Lane Denizen: It's hard to tell whether this is better with Fathom Seer or with Drakewing Krasis, but either way it's pure value. Absurdly good, and only its stats keep it from being an easy first-pick; at 3/3 I'd be windmilling him out of most packs. Note, as I think corsiKa missed, that this can put the counter anywhere, not just on the guy coming into play. It also doesn't work quite as well with evolve as you'd think, but that's a more complicated issue and I'll come back to it later.
Keymaster Rogue: the cost on this is actually surprisingly awkward when you only have Evolve guys to return (you never really want to curve, say, Cloudfin into Crocanura into Rogue), but a 3-power unblockable guy at 4 is always going to be viable, and the removal is lighter than normal this set. Another great target for Ivy Lane Denizen's counters.
Metropolis Sprite: Unfortunately, this is no Frostburn Weird any way you slice it. A 1/2 flyer for 2 isn't playable straight up, and having to burn the mana to make it a 2/1 is a pain in a color-pair that looks like it ideally wants to curve 1->2->3->4 most games. I might play this but I'll never be that happy to.
Scab-Clan Charger: The Bloodrush ability is unexciting but highly useful (and will push your flyers past spiders very well), but a 4-mana 2/4 is actually exactly what the deck wants to hold the ground and put another counter (or maybe two, with Denizen in play!) on a Cloudfin in the process.
Shambleshark: Fish Crab!
Slaughterhorn: see Scab-Clan Charger, but I actually think that's a better creature than this for the Simic deck, and sometimes even a better spell (though spending 1G instead of G on it is kind of awkward).
Spire Tracer: I suspect this will be okay, but probably the worst of the evasive options available. Certainly he's good with Denizen or Burst or counter-shifting, but so is every other flyer or flyer-like creature, and the others are all better on their own.
Burst of Strength: +1/+1 means it's not the best of combat tricks, but one mana is still fine, and untapping a guy means that your opponents will have to respect the ambush potential.
Pit Fight: yay removal. As corsiKa notes, the high-toughness evolve guys (Croc keeps coming up, doesn't he?) make this really nice.
Verdant Haven: IMHO this isn't as good as it looks. Going from 3 to 5 isn't that good in a deck that has several good plays on three mana, several on four, and very few on 5. The color fixing is really nice, of course, but I actually think this is much better for Gruul than Simic.
Notable uncommons, either good or bad:
Elusive Krasis: I have a feeling he's not going to be quite as good as he looks. The problem is that the natural Simic 'evasive guys plus ground-holders' strategy wants a lot of high-toughness, low-power guys to hold the ground... who are exactly the ones that don't trigger Krasis's evolve. It'll be easy to get a counter onto him and two should be common, but a 2/6 unblockable creature is fine but nothing-exciting because the extra toughness just doesn't matter much.
Hindervines: Hopefully, this will be a blowout; realistically, it's probably something like Safe Passage: occasionally blows out a combat step but surprisingly often underperforms.
Nimbus Swimmer: I expect X to be 3 or 4 most of the time. At 1 or 2 it's just not a great mana investment, and having 7 mana or more won't happen most games... though getting a dragon or bigger is always worthwhile. Maybe the best argument for mana acceleration.
Sapphire Drake: It's just a shame that so many games will just be over as soon as this guy gets cast. 'Evolve my two Crocanura, jump them, swing for eight in the air?'
Simic Fluxmage: This actually feels like a trap to me. Having this available means opponents will seldom have good blocks or attacks, but having to spend mana on it really stunts your development.
Urban Evolution: You really don't need me to tell you why 'draw three cards' is good, right?
Wasteland Viper: Weirdly awkward; the combination of higher toughness and deathtouch is really what you want on a blocker, not an attacker.
Ivy Lane Denizen and Evolve:
The gotcha I mentioned above is that even if you do put your Denizen's +1/+1 counter on a creature coming into play, that counter will never count towards evolving something else; for instance, if you have an unevolved Crocanura (1/3) and an Ivy Lane Denizen in play and then play a new Crocanura (1/3), you can put the +1/+1 counter from the Denizen on the new Crocanura but the 2/4 Croc won't let you evolve your 1/3 one (i.e., you can't end up with two 2/4 Crocs). The reason for this is twofold: (a) Ivy League Denizen's ability is a triggered ability, so it doesn't go on the stack until the creature is in play (the creature enters play as its 'normal' self, not with any +1/+1 counters), and (b) even if you stack the triggers so that Evolve goes on the stack first and resolves last, the condition for evolve (that either power or toughness is higher) is checked when you try to put the triggered ability on the stack as well as when it resolves - and if the condition is never met, the ability never triggers. (this is, roughly, rule 603.2 in the Comprehensive Rules.)