Thu'uMic (using your real voice and a microphone to make a shout)
Darker dungeons or perhaps one of the post processing mods
Better sorting (actualy.. im working on the assumption that nobody in bethesda knows how to make a ui in the first place.. i will just leave it there)
Many, many texturemods- The ones that stop faces from being blocky are amongst the top. Why did such a simple and obvious mistake go unfixed?
IShouting at my PC isn't fun for me, I rarely use shouts to begin with and having to actually use them in that fashion would severely hinder the times at which I could play.
UI design I can definitely agree too, overall it's relatively clunky, but...I suppose, the bright side is: it can ALWAYS be worse, right?
I'd agree had you said deeper dungeons -- my one big gripe about dungeon is: there are just way too many short, small and linear ones. I'd prefer a bit more variety to them, in terms of depths. Some nice quests therein would be an added bonus.
As for darker, in general, immersion only goes so far. I'd rather not have my face pressed up against the monitor to actually see where I'm going. Same goes for night time, while certain mods take night time to an ultra realistic level, I'd rather not spend time fumbling around aimlessly because I can't tell one point from another.
Texture mods should be part of, well, the modding community. Bethesda, like Blizzard, choose to make the game run on a wide variety of PCs and consoles, not just the bleeding edge. This is a choice that allows a much wider range of players to experience it. Even in it's defaults, the game is still very, very nice, and you add post processing effects like ambient occlusion (doesn't require a mod), certain ini tweaks, and even forcing AA/AF through your graphics drivers yields a much crisper and cleaner image. Mods only go so far.