Resistance 2 and 3
Really? Maybe its just me but I preferred Fall of Man to both of those. 2 I found was too melodramatic (plus lack of weapon wheel and co-op Campaign was a huge turn off) and 3 was just too bloody dark. Fall of Man was perfect IMO. Anyway, to each his own so I digress.
People have covered the major must haves. I would certainly add Infamous to hose that have already been said (I dont see it anywhere) as its definitely one of the more underrated games out there on PS3. I would also say L.A Noire is certainly worth taking a look at. It gets a bit annoying at points but a great game to really get immersed into.
So yeah, check those out. people might have mentioned them but Im not sure. I was trying to bring up some that werent said a lot.