here's a trimmed-down version of my post from the old PS3 thread:
brinstar wrote:Haze 4/5 - good action, good story, but too short
Assassin's Creed 4/5 - great story, good action, awesome environment. gets a little tedious though - pickpocket this guy, beat up that guy, kill him, rescue her. blah blah blah.
Army of Two 5/5 - really like this so far, haven't finished. also haven't tried playing without a friend, so i don't know how good the CPU ally AI is. customizable weapons ftw!
Uncharted: Drake's Fortune 2.5/5 - didn't care much for the mechanics. also, about 2/3 of the way through it turns into Resident Evil: Abandoned Power Station with superfast zombie shit. wtf?
Resistance: Fall of Man 3.5/5 - good enough game, but something felt missing. can't say what.
Ninja Gaiden Sigma 4/5 - great physics, awesome graphics and tight play control. hard as FUCK though, i still can't believe i beat it
Metal Gear Solid 4: Guns of the Patriots 5/5 - if you ever played any of the MGS games, you'll love it. as always, the storyline is convoluted and confusing, but even despite that it's a great game
Battlefield: Bad Company 4.5/5 - fun as hell. supporting characters crack me up, too.
in retrospect i'd rate Army of Two, Resistance, and Haze lower
since then i've played:
Dead Space 4.5/5 - scary space survival FPS. cool weapons, creepy setting (think Event Horizon meets Resident Evil). dozens of ways to die lol
Grand Theft Auto IV 4.5/5 - pretty fun. sandbox-style game with tons of sidequests, which is good for when you want to take a break from the main storyline.
Resident Evil 5 4.5/5 - very well done, see above comments about MGS4. one caveat: it has forced co-op like Army of Two, so you're probably better off playing with a friend instead of trusting the AI buddy.
Conflict: Denied Ops 1.5/5 - don't bother, seriously
Resistance 2 3.5/5 - improved a bit over the first game, but they removed the 2P split screen co-op capability which is a big drawback if you have a regular gaming pal like i do.
Borderlands 5/5 - love this game. shitload of randomized weapons, great action, hilarious dialog. interesting Diablo2-like skill trees for each of four classes provides multiple ways to play. decent replay value too.
stuff still on my list:
batman arkham asylum
ninja gaiden sigma 2
valkyria chronicles
whenever FF13 comes out
modern warfare 2
hope that helps