http://www.youtube.com/watch?v=fZ97I2p4_YY
Daggerfall had a way to put music, not only in places you where, but also with what is happening. Music for the night, music for the snow, Music for sunny days etc.
I think a return to that kind of thing, instead of just 5 musics looping dependeing on where you are (and if you are in combat) would be awesome.
Actually, I think that Combat music isn't so great. You can't get surprised anymore like you could in Daggerfall, with creepy music, you go for a right turn, realise you are going the wrong way, turn around and ARGH! How long have that damned vampire benn following me?!
I think combat music should just be there for epic fights, like agaisnt dragons or very powerful guys. For the rest, leave the music act as the seasons slowly change.
PS: please bring back the "snowing tune" from Daggerfall!