I've started and very quickly abandoned a number of games, like Deus Ex, Dead Island, LA Noire, Uncharted 3, and others. It's not that I didn't like them (except LA Noire), it's just that there were too many games, not enough time. I'll certainly go back to all of them eventually.
As for what I missed completely, I haven't bothered with Assassin's Creed:R yet because I haven't really played Brotherhood yet. And I haven't touched Skyward Sword yet because I want to get through Twilight Princess first.