The main thing I disliked about Oblivion was the main story, which paled by comparison to the awesome guild quests. Going through the portals to the hell island/tower things got old quickly, and whever too many NPCs were involved in a fight the game just went full retard. I'm hoping these issues will be addressed.
Beyond that, I really enjoyed it, right up until the day I burned out right in the middle of Shivering Isles and never played it again. But I had played it for hundreds of hours before that. I guess I'm sort of the opposite of Pants, I love games like this - wandering, exploring, completing all the side quests, scraping together enough points to advance to the level. The endless quest to level up always drives me more than anything.