My vote for Rayman 2.
Eric Chevalier is a professional artist who compose soundtracks for a few full-length movies.
Rayman 2 OST is one of the most sophisticated and film style soundtracks in games I ever heard.
And it was released in '99. (1st track comes from 97').
But in-game compression deteriorated proper perceiving of a work, which work in fact, was deeply sophisticated in a form and content. Some kind of a film style.
I put plenty of effort to release 44kHz version from PSX, and remaster it, and Revolution songs, to prove that this music has so much big potential, is so inspiring that it always deserved wider recognition. But it still requires more effort and better equipment to master files enough to show it's full potential. It is definitely not finished.
You can try to listen the soundtrack once again from my link (signature), in this better quality, if you haven't done so, if you wish.
Rayman 3 was too chaotic, and childish in form imho, samples were less sophisticated, but content was much bigger, and it would turn out that half of the song's which I really, really love from R3, states half of a R2:TGE OST content in duration.
Droolie said one thing that I agree with:
Rayman 2's soundtrack focuses more on creating a unique and adventurous atmosphere for the game, but it's not as melodic.
And this "melodic" is just sometimes foolery for me in a form.
Maybe I'm a little angry on R3 OST because we just extract R3 OST from HD version, which gives not that bad quality, but I'm still not happy with it's mastering, it is mostly 32kHz and it's hard material to do anything useful with it.
But, maybe, once upon a time...