Haven't played much of the game itself but the soundtrack has been worth the purchase alone imo.
I have to say that I have a bit of a weird taste of music and rarely like anything mainstream so this soundtrack is right up my alley. =)

I'm a big fan of the soundtrack as well, and while I do enjoy the game a lot, I find myself listening to the soundtrack more often than playing the game. I would say it does have a bit of a mainstream-ish sound though, or at least it somewhat reminds me of a mixture between the work of The Prodigy and NIN. (without vocals, of course)