Music would be tolerable if it were possible to turn it off.
Alien Arena is a good example of this. At least one map has horrible, terrible, ear-gratingly bad music built into it. It's not really a bad map, but the music is so terrible you don't even want to play it. Ever.
Nexuiz, though, has done ok. The music is relatively quiet and pleasant. It makes good background music, and is easy to ignore if it isn't your sort of thing, although it in no way fits gameplay.
Of course, both of those are hyper arcade action adrenaline rush sort of games where gameplay moves along so fast your character doesn't make any sort of noise.
I need to be able to hear all them damn bugs chittering around, so I really think Tremulous is best off without music.
