1st off I hope to see some skills back.
Spears, Axes should be Axes again, not blunt by even close. Blade was not so big issue, but I still think it was better while small and big blades were separate.
Armor- medium may not be as useful, but unarmored is very important. It should be vital for any monk, and most of the mages would profit from the skill.
Enchanting should also be back I think.
Leveling should be toned down, so that non of the random bandits own too good equipment.
Gold should be much more common. You should remove gold and too worthy item from leveled free city junk. In oblivion going trough one Market District run would net me around 4-6 hammers, around 30 gold and handful of ingredients, on average.
Traders shouldn't have infinite money, but should have like in Morrowind, daily sum. Also it would be nice if randomized sum would be given to them, so that players don't strategically visit certain traders only because of the exact money they have.
Artifact quests shouldn't be restricted by level, but only by how hard they are. (So player can try to get Goldbrand at lv 5, but realistically he would get killed easily before lv 20. Also there should be more hidden treasure and artifacts like they were in Morrowind, unlike in Oblivion where ALL artifacts could only be found by quest (except Umbra, which wasn't even count as an artifact).
There should be an aditional journal or something, where player could write his own stuff down. I know I often wanted to write something down, and I had to use a note of paper. Would be nicer if I could use all the feathers in the game for something. Same thing would be really cool for maps, we should be able to mark the map ourselves. Maybe even no markers like when we found some random Fort or Daedric shrine, maybe to only be able to mark it ourselves (except towns player should know about, ofc).
Dialogue should be much more improved, in both Oblivion and Morrowind people were talking about same thing too much. Like in Morrowind, rumor about cold island Solstheim would stay for the rest of the game, and in oblivion we would listen about destroyed Kvatch half of the game, just like since I finished Knights of the Nine, I had to listen for the rest of the game that I am not what people thought I am lol.
......had much more, but forgot, will write it down later
Edit 1:
Bosses and hard creatures- there are no real boss fights or strategies. I always won by simply running in, throwing a couple of huge area spells, or would swing a sword and that's it. There was never need for extensive heal, poison spell or poison effect y a weapon was never lethal enough that curing it instantly would be only way to survive. I never had to cast too much protective spells, and or cast debuffing spells or enemy.
Also some really tough enemies should have very large resistance list, so that only few things could beat it wit ha bit of strategy usage. There are no enemies you utterly fear of, for example Vampires could have been the only threat in all TES games because of the chance to catch vampirism, or ghost creatures because of not being able to hurt them easily. However that threat was never real since fire/magics or silver+ or enchanted weapons were always so numerous that there would be no creature you couldn't harm early in the game.
Hmm all for now