I find that mainstream games rarely hold my attention for very long, or if they do, I end up hating them. I like the indie scene a lot more, some really cool stuff comes out of it. There are a few "mainstream" games that I still like: TF2 (which hardly counts, considering Valve still has the sense of community of an indie group), Batman Arkham Asylum, the Assassin's Creed games (though they wear stale pretty quickly), and Just Cause (I don't know why, just plain fun).
Everything else I play and I may enjoy for a little while, but I usually end up getting sick of it. Quickly. The most notable games for that were Oblivion, Far Cry 2, and Fallout 3 (Oblivion with guns, just awful).
I'm probably the only person here who didn't like Fallout 3 of course. Sorry, but the mechanics are crud. I could have designed much better action RPG mechanics (I have, actually?). NPC interaction was bad, and the environments never felt believable. The larges city is Megaton, and it's tiny. Megaton is the size of a large house. A self-sufficent city that does not make.