1. Technology: From a technological standpoint, don't suggest anything "higher up" than guns, even the most simplistic gunpowder guns. Tamriel is essentially stuck in a specific period of time. It's sort-of like Fallout 3, in that "What would happen if America progressed technologically, but stayed in the 1950s era?"
2. Model/Animations: Don't suggest something like, "I want to see 50 different kinds of sitting animations"
That's pretty much it.
My suggestions:
-Much like in Oblivion, I would like to be able to at least see the major cities when opening my map. For new players, it was a pain in Morrowind to have absolutely no idea where to go; you pretty much had to hope you were following the right trail and didn't take a wrong turn at someplace.
-If a Hero becomes famous or infamous enough, townsfolk could whisper rumors about how famous or infamous the Hero is, or what important accomplishments he's done.
-If a Hero can own a house like in Oblivion, have it serve more purpose. Maybe certain houses can have upgrades like putting in a forge.
-I really liked how you could find an Adventurer in random dungeons in Oblivion. I'd like to see this in Skyrim too.
-Please don't leave two handed weapons in the dust like you did with Oblivion.