If I could just recommend 1 ps3 exclusive it would have to be uncharted 2. It's by far the best game I've ever played on any system in any generation. The graphics are pretty good (a little dated by todays standards), but the fluidity of combat, hiding, movement, and verticality is second to none. Of the 4 BIG PS3 mature exclusives (uncharted, GOW, Killzone, and infamous), I'd have to rank it the 3rd best in terms of graphics, but the overall best game of 4. It's my 1 favorite game of the last decade and a lot of good games came out from 2000-2009. I'm also no PS3, fanboy. I'm an equal opportunity gamer (I own all 3 consoles of this generation and pretty much every generation) and I can say without a doubt that uncharted 2 is the best game I've ever played bar none.
God of War 3 is an excellent entry into that series. The game play isn't midblowing (it plays like any other GOW game, but the graphics and scales are unreal). At one point you fight a character who is so large you're the size of his finger nail. I hope it doesn't sound like I'm ragging on the gameplay. It's top notch, but it isn't evolutionary like the first god of war. THe graphics and character models are easily the best I've ever seen. That includes some PC games. Cratos and all of the various gods and mythical creatures look amazing. The general bad guys (i.e. the guys you fight in large numbers) aren't all that impressive to look at but thats made up for by the huge amount of mini-bosses and bosses who look great.
Resistance 2 is pretty damn good. I like it a lot except for the fact that there is no way to brighten up this game. It's super dark which is kind of annoying. To see anything I have to change my TV settings.
Besides that most of the games I like on the PS3 are cross platform releases. The xbox has really owned this generation in terms of exclusive releases (mines been long broken
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One game I can't recommend is Killzone 2 (something about this game is just broken to me). Graphically it's easily the best looking game of this or any generation on a console. I really don't think I've seen a prettier looking game on any system. It lived up to the PS3's pre-launch hype in terms of graphics. However the gameplay just isn't all that fun to me (uncharted 2 is way more fun). All of the control options suck IMO and none of the guns have that wow factor.
Bottom line it's my opinion if you own an Xbox 360 and don't care about the ps3 exclusives then don't buy one. Xbox has way better exlusives in terms of games and DLC. Most PS3 games are on the 360. I will recommend a PS3 if you want a bluray player, a reliable system that won't breakdown (my launch system been like a tank), and if you want free online gaming. Seriously paying for online gaming is just dumb to me. These reasons alone are why I won't rebuy an xbox.