I'm an action/platformer guy at heart. Some of my favorite all-time series would be the original Spyro Series, the Ratchet and Clank series, and the Jak series. I replay games a lot so my favorites have stayed fairly consistent over my life. Other favorites include Resident Evil 4, God of War series, and OG Guitar Hero games.
Recently I have played Borderlands 2 to death. I don't think I've ever played any game as much as I've played that game right after buying it.