Yes, music in a game played for dozens of hours must be done correctly. This game comes up a little short in that respect.
Variety is essential, as the OP has said. More than that is required though.
MUSIC MUST NOT ATTRACT THE ATTENTION OF THE MIND. If that is what if wanted, then turn off the pc game and put on some headphones and close your eyes to be totally into the music.
This is a strategy game, with the mind juggling hundreds of facts that change with each turn. There is no time to listen to music and hold all those facts in place.
MUSIC SHOULD BE A BACKGROUND MOOD ENHANCER.
The music volume should never change. This game has failed at that respect. I should never have to change the volume dial on my speakers. Soft music and thrilling music must have the same volume.
Never repeat notes or phases. Repeating patterns attract the minds' attention. Only one song in the game has done this so far, and that song has caused me to turn off the game music and put on my own cd music.
Change the music often and quickly We all have our own personal tastes in music. I can put up with a sound I don't like for a few minutes and no more. I would say about 2 minutes per song, but that is just my opinion.
Way back in the 90's there was a game called Sid Meier's Colonization. In that game we could open up the music list with one click of the mouse. It showed all the music selections and what was currently playing. We could skip any song we did not like, or just select the one we wanted to hear.
STARDOCK Please implement that ability for this game. And allow us to disable any song we don't want in the music list.
Another improvement would be to turn off/down the game music when a special effect sound is happening. Like enchanting a city. The game music overpowers them currently.
These are my thoughts on music for a 4X game. What are yours?