I will chime in and add that I too don't get the music playing in-game (except indeed in level 1 where it plays for like 1 min and then doesn't repeat).
For me that is kind of a deal breaker: the game has moments where sound effects do the job adequately, but in many instances it can be completely silent (different from Half-Life for example, where there is little music except for specific points and the game's soundscape is designed around environmental sounds).
EDIT: so I played the game with the soundtrack playing in a separate music player at relatively low volume compared to the game audio - imperfect solution but better than not having music the vast majority of the time - that said, there are various moments where the game triggers a track, in which case it covers the soundtrack from the music player so long as you set the music player to a much lower volume.
Post edited February 12, 2020 by Sat42