Besides the Halo franchise I'd say:
Paper Mario and the Thousand Year Door. It was insanely fun going through the game as Mario who recognizes that he is in a 2D world with other 2D characters from the Mario Universe and it has an AMAZING adventure and storyline with incredibly addicting turn based fighting style and boss battles. Seriously, if anyone still has a Gamecube and is bored of what they're playing right now and are looking for something fun to get you to Halo 4 or whatever you're waiting for this year pick up this game if you can find it. IT WILL CHANGE YOUR LIFE.