Oh man, I'm probably most excited for the My Castle part of the game. It looks like you can do a lot of fun things with it, and it'll be nice for when you want to take a break from the main game!
Other than that, I'm pretty excited for all of the new classes/skills/maps/weapons, gay marriage, the music (Awakening's was pretty good, so I have high hopes for Fate's music), and all of the new/returning characters!