i was having this problem too: there are so many genres with id3 (alternative, alternative rock, classic rock, indie rock, etc.) i kind of gave up on the thing. eventually, i want to assign them the genre that allmusic.com uses. interestingly, they assign a genre, and a style. check them out. i am currently searching for a tool that would auto-retag all my music based on lookups into allmusic.com

good luck
-ted