Is this restricted to soundtracks which you can download separately, not any ingame music?
For instance, Fallout Tactics comes with a separate downloadable soundtrack, but IMHO the best music in it (the Junction City battle music) is not included, among many other pieces of music I guess. However, you can listen to it without playing the game because you can find the mp3 file within the game installation.
https://www.youtube.com/watch?v=FM6e0lvgtAY That said, I also sometimes have problems listening to music without knowing or playing the game. If I just tried to listen to Starcraft music, I'd probably find it slow and boring, but when you listen to it in the background while playing a long mission, it sets up the mood perfectly.
I tend to be less patient if trying to listen to music without playing the game, as then I expect the music hook me during the first 10 seconds or so. Like the linked Fallout Tactics music, without playing the game I would have probably listened to the first 10 seconds and then pass it as too slow and boring (it gets much better the longer you listen).