At the time, I'd have to say that Super Mario Galaxy was probably my favorite game to release that year. Some of these I didn't get to play until later on for some reason or another -- possibly because I didn't have much income for myself or didn't spend money wisely, but I think part of it may have been that games weren't quite so large in my life at the time (film is and remains my biggest passion).
Looking back from now... probably still Super Mario Galaxy. But I have a huge fondness for Rock Band, Half-Life 2 Episode 2, Portal, Super Paper Mario, Uncharted: Drake's Fortune, and Metroid Prime 3: Corruption. Some of these I ought to revisit (MP3 especially), and others I've yet to touch at all. What a fucking year, though.