Both Mass Effect games. I'd also recommend any of the Halo titles you can get for under $40 (your currency sucks, get a proper one etc.). Both game series have replayability to an extent - Mass Effect, being an RPG, has more, but I played Halo 3's campaign 5 times over before I got bored due to the somewhat nonlinear combat - and they're both great fun. And also, they're sci-fi space operas on strange and interesting new worlds, with intriguing backgrounds and art styles (Mass Effect has the better background while Halo has the better art style IMO). Word of warning, Mass Effect 2 and the later Halo games won't make a bit of sense if you don't read up on the background or play the original(s) first.
