First of all, the music in Civ4 is awesome. Every time Baba Yetu starts playing and the sun rises on the opening menu right at the first crescendo, I think "this game is awesome. It's not some stupid shooter or action game: it's about humanity and history and the rise of civilization and it rocks." And then I see the cartoony leaderheads and I'm brought back to reality (which still rocks).
Anyway, I'd rank the music as follows:
1. Medieval
2. Renaissance
3. Industrial
4. Classical(i.e. Ancient)
5. Modern
I love medieval music in general (in real life) and I adore the "El Grillo" song. The Renaissance and Industrial music is just good, classic classical music - what more can I say?
There's only one ancient song I really like - the "AncientSoundTrack2." The other ones are just slow drums and bells as far as I can tell.
I actually like that "the people are the heroes" song, but it's just so disappointing that the modern soundtrack has no jazz, blues, big-band, rock, or even hip-hop (not that I like all those kinds of music, but they are representative of modern times!) that I can't put modern anything but last. I guess copyright and royalty fees have led to the limited selection we have now. Does anyone have any ideas for good 20th century mix I can put in my "modern" folder?
I really didn't like the ancient music in Civ3, so much so that I turned the music off in that game and never turned it back on. Apparently I missed some good modern music doing so!
Finally, one critique that could be made of Civ4's music that I haven't seen in this thread is that from Medieval on the music is VERY euro-centric. I mean, like I said, I love medieval European music and can't get enough of a good Gloria or Psalm 95 or whatever, but when I'm playing as the Aztecs and I'm Buddhist, it's a little funny to be listening to Christian music...
But I guess Ethnically Diverse Music Styles is a little too much to ask for!