What about theives guild, dark brotherhood, companions, mages' guild, the vampire expansion, and Dragonborn? If you haven't played any of them you're really missing out, each and every one is fucking awesome. Never mind all the miscellaneous side quests, Daedra lords, all the different Holds, levelling up your character... The sheer quantity of content in Skyrim is mind blowing.
But then again, Fallout is a huge game too.
I like skyrim personally.