I thought the music was ok, but I eventually switched it off. Eventually, you hear all of the tracks a sufficient number of times.
One thing I do wish more games would do would be to provide a "Music Playlist" under sound options someplace. Since everyone has different musical tastes, I imagine everyone would have one or two tracks on any game they would just as soon disable, so they could enjoy the rest.
My PC has both a CD-RX and DVD drive, so I currently have Civ 3 in one drive and a music CD in the other. Having the speakers pipe out battleships, artillery fire, wolf howls, AND Handel's Messiah simultaneously is really rather cool...
Cheers,
Stilicho