I had a lot of fun with the likes of Crackdown, Musou Orochi, Phoenix Wright 3, Dracula X, Bioshock, Arcana Heart, Virtua Fighter 5, Mass Effect, Super Mario Galaxy, Sengoku Basara 2 Heroes, and a lot more, plus there's games I've only just begun like Crush, Tomb Raider Anniversary, Uncharted, Shin Sangoku Musou 5, Unreal Tournament, and shit tons more, but probably the most fun I've had this year has been with Halo 3. The multiplayer, particularly the deathmatch modes, give me tons of fun every time I load it up, be it by myself or with friends, and that's all that really counts in the end.
My backlog has only grown ever-larger this year, too. So many unplayed or barely touched games.

I need to kick this habit of buying new games when I have yet to finish others.