2. Portal 2 (Xbox 360, PS3, PC, Mac)

As funny as it is cerebral, Portal 2 gave gamers exactly what they wanted out of the follow-up to what developer Valve originally included as a bonus add-on to 2007's The Orange Box. The cult-classic turned mainstream success story presented us with new mind-bending levels, great celebrity voice performances, and a fascinating storyline. All this combined with impressive an co-op mode and a healthy amount of DLC makes Portal 2 easily one of the year's best.