All I know is that Oblivion has been a real disappointment from Bethesda. I mean Morrowind was superb, Tribunal not so much and Bloodmoon again was epic. But, neither of these could compare with Dagerfall. Now that's an RPG.
The only thing Oblivion is better at then it's predecessors is the AI. Graphics can easily be tweaked using MGE for TES 3 to make it look exactly like Oblivion, LOD and all. The combat system was better, in my opinion, in TES 3. And another thing is that Morrowind's CS is a lot better than Oblivion's. Oblivion's can't even handle proper lyp sync nor can it manipulate 3d sound.
What I would like for TES 5 is either Elsweyr or Akavir(preferably Akavir). Skyrim would be similar to Solsteim I imagine. Black Marsh is... a plain swamp. Summerset Isles might be nice, but I imagine it would be filled with Daedric ruins which I'm pretty sick of. Valenwood might be nice.
Anything exotic would do. I don't want to play Cyrodiil which was made so badly. I mean come on, Blackwood and the Great Forest were terribly made. We were lead to believe they would be exotic places, a dangerous murky swamp and an exotic rain forest. At least Vvardenfell was done properly and it really did feel like an alien world. The Shivering Isles were good, though.
Oh and another thing: Fast travel, map quest markers and the leveled item/creature system completely ruined the game. Also, the story is very linear, whereas in Morrowind you had several choices on how to some quests. Not only that but a lot of things were affected based on your race and the guilds you were in unlike in Oblivion where there was no connection between the small number of guilds.