The ability to toggle realism
I like the way Bethesda went when they made Fallout 3, I've played Oblivion for hundreds if not thousands of hours and I'd always wanted to be able to tear bodies apart, I know Elder Scrolls has been more of a kids game (in some peoples opinion) and blood and realism hasn't been emphasized, but I agree here in that a realism switch in the options menu would kick some major [censored], the ability to splatter an opponent with a magic spell, or to watch blood drip from their neck when you drink your way to total vampirism, or even werewolf, and to see scars appear when you swipe with a claw. To knock heads off an watch them roll before stomping them to a fine sticky mush and scraping them off your boot... Ok, maybe too much realism, maybe not...?
I'd also like to see more variety in the way of weapons, sure, you've got your bows and swords and clubs and bare hands, but why not have a magic gun of some sort, and staves which not only have a magic effect but can be swung as melee weapons also. Explosive arrow heads would be nice, and maybe some barbed arrow heads so that when you rip them from the flesh of an opponent blood flies everywhere.....
Stephen.