Super Mario Galaxy 2
This is my personal favorite game of 2010 for many reasons, all of which you can read in the review I wrote back in May. In a nutshell: It's the best Mario game ever -- in my opinion, but I've been told I'm not alone -- and can pretty much claim the title of best-ever platformer while it's at it. The experience is magical, the design is masterful and if there were one game I could be stranded on a desert island with ... well, this is it.