I remember when I beat oblivion and the expansion. It was pretty fun, though the leveling system is broken. It was very, very hard to get 100 in every attribute (trying to get a +5 increase to three attributes per level is takes a lot of time and patience), but with carefully planned and calculated training, you can do it.
The game is so big that I never managed to complete all the side-quests. Most of them, I hope though. I got about 450 hours of gameplay out of it before I finally got bored.
Please feed the trolls. XD