I would recommend Borderlands 2, depending on what you didnt like about the first one.
If the lackluster story and drab enviornments got you down in BL1, BL2 is light years ahead. If it was just the gameplay or loot, graphic style, humor, and such, then maybe not so much worth trying again.
Also, there a new game called Fuse coming out in a couple weeks. The demo is available on xbox live and it will be up to four player co op, sci fi TPS type game.
Also Dead Space 3
Resident Evil Operation Racoon City. I love the game personally, but it seems to be a love or hate type of game.
Resident Evil 6 also, same seems to be love or hate