I can only refer to the games that are also on xbox 360.
As mentioned Bioshock 1 & 2 were great if you like horror survival games, Fallout 3 & New Vegas are just friggin great epic RPG/shooter crossovers (mainly RPG) & Borderlands is all kinds of fun. The best game across platforms has got to be Red Dead Redemption though.
For something a little different and family appropriate, Ghostbusters is pretty great too. I bet you could probably get it pretty cheap.
It's not for the easily frustrated. I had a bunch of problems with the flicking motion needed for stuff like the ping pong game. I really *wanted* to like it, and I'm sure that if you spent enough time with it you'd get really good.