I'm not really sure myself. I know Jeremy Soule (Secret of Evermore, Icewind Dale II, etc) was assigned to compose all of the tracks for orchestra, which he did very nicely. Why there were no area themes or event themes, who knows?
And *stop* crediting it as an XBOX game! It's a PC game ported to the XBOX to satisfy those console freaks who don't have powerful enough PCs. =P
I really must repeat what has already been said above... if you haven't played this game... PLAY IT!!! It is awesome super-ness. The game is so completely open-ended, you can kill whoever you want whenever ( that's if you're skilled enough not to get killed first =p ), you can progress through the game as a theif, a robber, a mage, a glory-seeking warrior, and so many other possible ways. Any item you see onscreen, you can pick up and use, be it mushrooms & moss in a field or the weapons lying around in a amoury shop ( though that would be called theft =p ). Huge game world, so detailed, you don't even have to follow the main quest if you don't want to... GET IT ALREADY!!!
^^