I recently downloaded Castle Crashers, I heard a lot of good reviews from people. I know it's been around awhile. Really fun multiplayer game.

Also dl'd Trine 2, after reading a good review in Game Informer. Amazing visuals, lots of depth and color and artwork for a side scroller. Good mix of character abilities, and using them for puzzle solving. Can play up to 3 at a time, but if you're playing alone or 2 up you can easily swap characters. This is the type of game I could enjoy just as much watching someone else play.