echoing rdr, rockstar at their finest. the multiplayer is also excellent, so's all the dlc (undead nightmare especially -- it's like a whole new game)
i'd also recommend checking out the assassin's creed series. really high production values, great gameplay, story, etc etc. the multiplayer in brotherhood is also amazing, probably the best/most innovative and interesting multiplayer i've seen in a long time. start from the start though!
demon's souls is an incredible title, but prepare to have to stick with it. it is very unforgiving, and you will die, a lot. brilliant, though. rally atmospheric, interesting multiplayer (both co-op and pvp, if you can consider there to be a separation). sequel also looks promising!
most everything out there on gtaiv speaks for itself, i think. another great title, rockstar again, etc etc
with that in mind, pick up la noire!
i hear really good things about bayonetta, and i had the first god of war which was the greatest action game in a long time, so no doubt god of war 3 is great, though you may have to do some backtracking. uncharted looks promising, but i hear the first one's not so hot?
borderlands is pretty cool, but i found the environments very samey after a while. i'd also recommend it on the pc over a console, if that's an option
lbp2 is excellent, though you probably figured if you own lbp
ico and shadow of the colossus on ps2 were two 10/10 hands down games, and i think they were remade for ps3 at some point, so pick those up if you've never played them. trico/the last guardian, the next in the series, also looks to be amazing!
Just a warning Mirrors edge may look good visually, but its absolutely terrible. Repetitive,horrible camera, and very short you could finish it in a day, doesn't really have replay value either.
haha, uhh, if you're slamming mirror's edge's camera, you're kinda slamming all fps games. how can the camera in a solely first person game be bad? it's a solid title. beaautiful visually, great music and ambience, solid atmosphere. it is pretty short, i'll give you that, but the atmosphere alone gives it replay value. as with borderlands, though, i'd pick it up on pc