strider is a pretty good platformer
sanctum 1/2 are pretty fun with friends
q.u.b.e is a nice little puzzle game with neato mechanics, only a couple hours long so you can beat it in an afternoon
metro 2033 is fantastic. people say you shouldn't play through it on ranger difficulty the first time around but personally i think its the best way to play
e.y.e: divine cybermancy is clunky, ugly, has an absolute mess of a storyline, and is also one of my favorite rpgs due to how insane it gets