If I could only give you one game recommendation it would be:
Uncharted (best characters in a video game this generation for me so far) You need to play the first before the sequel hits this Fall. I think Uncharted 2 will be one of my favorite games of all time!
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Action/Adventure runners up:
I would say MGS4 purely for the cinematic and amazingly high production values even if you haven't played the first 3.
Resident Evil 5, but only if you have a friend to play it with co-op.
Batman: Arkham Asylum - try the new demo on the playstation store, it convinced me to buy!
As for RPG's: I think Demon's Souls could fit your tastes when that releases in 2 months. As others have said you might like Folklore and Disgaea 3 for your RPG strategy fix. Watch for White Knight Chronicles and Borderlands in the future too. Borderlands combines RPG with FPS.
PSN: Get PixelJunk Monsters & PixelJunk Monsters Encore if you like tower defense games (2 players local co-op only).
Bionic Commando Rearmed was excellent as well.
