Levitation.

I want my damn levitation back.

Map size.

I'd pick .................... my nose ....
Seriously though , climbing was awesome we want climbing !

Scope of the game world.

Climbing by far, especially considering Skyrim's geography.

I would bring back character traits. weaknesses, strength, expertise/disabilities, forsaken types/matierials. that stuff.

would be nice to play as a magically-disabled breton again.

or an imperial that's greatly afraid of rats.

or a nord that is so skinny he can't lift 2-handers.

makes for interesting characters with flaws and strengths.