Yeah, Mass Effect! Since ME1 didn't get a PS3 release, you need to read the story or watch a whole playthrough of ME1 to help you decide in the PS3's Mass Effect Genesis. It's a free DLC interactive comics that's included in the PS3 version.

Also try Dragon Age 2, which is imo, a medieval version of Mass Effect. I didn't play the first Dragon Age but majority says that it's the better game than DA2.

Splinter Cell and Tomb Raider games.

As for AC-ish games, Thief: Deadly Shadows is one of the best out there. It has that scare factor even if it's not a horror game. No PS3 version though, but you don't need a powerful modern PC to run it.