2010 was the year that iPhone gaming rocked my metaphorical world. I've probably spent more time on that device than any other, mostly on Words with Friends and Carcassonne, both of which made excellent use of the internet capabilities to provide a polished game played against real people. Pocket Frogs was another highly addictive experience that benefited from being able to trade frogs with friend. Other games like Ravensword and Infinity Blade showed off the possibilities of complex 3D graphics and open world game play.
However my two contenders for game of the year are both on the Xbox.
Red Dead Redemption was a superbly constructed game that pulled in just about everything that you could ever want to do in a Western, in much the same way that Larry McMurtry's 'Lonesome Dove' paid homage to all of the familiar tropes of the genre. The multi-player wasn't quite so polished as the single player experience, but one definite highlight was the co-op mission pack with a cattle drive through a canyon, across the open scrub land and into town, whilst fending off an attack from cattle rustlers. Superb.
The top spot has to go to Rock Band 3. I have enjoyed music games since Guitar Hero back on the PS/2, and this is the evolution of the genre into something that is very nearly perfect. There is a huge library of music available to download, numerous options for customising your avatar and band, a variety of challenges and of course the sheer visceral thrill of strapping on a plastic guitar and rocking out to 'Highway Star'. Worth every penny.