LEGO Star Wars
Posting because I'm playing III right now, but you can discuss any of them in this thread. Anyone else own a game from the series? I know they're simple but the gameplay is addicting and there are some genuine challenges if you look. It's kind of like Assassins Creed where you have to place some of the restrictions on yourself when you play to up the difficulty (i.e. no power-ups).
It's also mad fun co-op. The new ground battles are awesome with two players, since one person can take a vehicle, attack structures and lay down cover fire while the other guy commands and builds structures. The level of teamwork is surprisingly high. Then there's the random insanity that is versus mode.