I hate the game as much as i like it. It has so much potential, so much was wasted.
- Online coop, like 4-8 players max.
- A game world that makes sense, even if its only cosmetic (trading caravang travelling from town to town, some decent causality for your actions, some bloody common sense for NPC actions ect)
-horseback fighting
-Backpacks, seriously. Maybe just for cosmetic value, but as an adventurer i kinda expect to have one. Oh, and i would like to be able to buy a pack mule/chariot (park it outside and fill it with your excess loot when you are done raiding a place)
-Maybe : cities populated with NPCs that are just there (like assasin's creed).. you know, who wont speak a word to you and walk around doing their thing. SO a capitol can be full of people that run away screaming when you burn it down. I dont really like the way all npcs are important in the game, cities are empty.
-NPCs with more than 5 lines of text, that do more than just wandering around aimlessly and do some actual work (just some animation or whatever to show they are busy.. like carrying boxes/goods from A to B).
-Open world with cities integrated in the maps. Morowind did this IIRC? Only played it briefly.
-improved mod support and mod-tools. I want to mod blaster guns in the game

.. that way one motivated modder could change the world to fit another setting entirely.
- The ragdoll physiscs is broken; actors FLOAT in midair when they fall. Make them fall down like the 200 pound meatbags they are... and fix the way they keep their hand-held items in their hands even when dead.
Completely re-invented and re-balanced system:
1- The system in oblivion simply sucks. Magic owns.. EVERYTHING, and makes warrior and rogues build absolutely obsolete. You CANT win without magic in that game. Warriors and rogues stop being viable around level 20, where no matter what you do.. ennemies take 10000000 hits to die, and mages are simply superior to you at everything, constantly.
2- being a warrior or rogue should be as effective as a mage in the endgame. Assymetricaly equals.
3- Ennemies should not scale in level with you too much (that glass armor on bandit nonsense).. the OOO mod system worked quite well for this.
4- No skill should ever be useless (there are too many useless skills.. like athletics ect)
5- leveling should NOT be most effective when you metagame and grind (the major-as-minors builds to maximise attribute gains)
6- HP should be given retroactively as you level up. why? Because you gimp your character if you dont maximise Endurance ASAP.. this kind of "must do to not suck" are there only because the game is poorly designed.
7- i would not be against some significantly increased leathality in the game if it means that late ennemies dont need to take a billion arrows/sword blows/fireballs to die. When i sneak up to someone and let lose my top-quality arrow in their skull, i want to see a dead body the next moment.. not a charging, angry imperial soldier with 10% less hp...
-7A- Of course that means that armor should work differently, cuz right now its mostly useless because magical enchantments/spells does it better and at low skills level armor is too weak to be of use.
Maybe armor could give a set damage reduction (like 5)and a percentage of damage mitigation (say 15%).. so an armor like that against a 100 damage blow would first reduce it to 95, then reduce it by 15% to a total of ~85 damage received. Dunno.
8- Menus require too much of clicking useless "okay" buttons, especially when you do something you arent supposed to, just make it a floating text or somethign that dont break the flow.