So there's a lot you could nitpick about Oblivion, probably a lot that wouldn't require it's own thread. So here we are! I guess anything goes, story, gameplay, lore, whatever. Don't forget to throw down  spoiler tags if necessary.

So uh, something that bugs the hell out of me is that the imperials don't seem to have any kind of military headquarters. You would think they would have a fort outside of the Imperial City. After all, the empire supposedly spans all across Tamriel. Where are these guys coming from? The Imperial City walls? huh? Unless I missed it, they have city defenses and that's about it.

and something else that bugs me, and I think that bugs most the people that played Morrowind, is that Cryodiil is pretty... tame. Morrowind was really unhinged. It was a political mess and you also got the feeling there wasn't a whole lot of civilization out there. Cryodiil is the opposite. All the provinces within are unified, all the major threats have been dealt with probably years before. Without this whole Oblivion thing happening Cryodiil would be in pretty good shape. The wilderness is call for adventure, but the ability to warp to any location at any spot in the game kills off any sense that you've traveled anywhere. That's not going to stop me from exploring all that stuff, but you never feel very far away from home. In Morrowind, at times it felt like you were truly away, and were horribly vulnerable.

yeah, the fast traveling pisses a lot of people off, but its hard to wander around to get where you need to go when you have this option.
The gameplay is fine.
What most people disagree with, and I guess I kinda agree with them, is that the world levels up with you including items. So you are on par with everyone and there is almost no challenge. Especially since you can change difficulty whenever you want.