Degausser on 29 November 2010
Borderlands.
Yeah it was 2009 but I only got it this year and I still play it with my housemate once or twice a week. It's just awesome, Gear Box are onto something special here imo.
If we go for a 2010 game though I'll say Darksiders as it made the Zelda formula I love so much feel fresh and new again.
