#4 Borderlands 2
Borderlands 2 was a game of excess, with an infinite supply of randomly generated weapons, a massive world to explore, and a heaping of DLC packs that expanded on both fronts. What it didn't have too much of was great storytelling or a satisfying endgame.
With next year's sequel, Gearbox is looking to fix those problems while simultaneously bulking up on everything that made the first game great. Borderlands 2 will explore new regions of Pandora, and this time they'll all be interconnected, rather than a series of discrete areas separated by cumbersome loading screens. To keep co-op fresh, they're introducing four brand new characters to replace the old set, each with their own weapon proficiencies and unique set of skills. They've only announced one of these new faces so far, Salvador the Gunzerker, who has the ability to dual wield any weapon in the game.
There's still plenty to learn about Borderlands 2 before it hits stores sometime in 2012, but with as many hours as we poured into the first game, it's hard not to be excited about whatever Gearbox has planned.