When I first played Fallout, I never really noticed the soundtrack. It's so much in the background, and that's what makes it so good. After a few years, I was developing a fascination with more ambient stuff and came back to the Fallout soundtrack and basically fell in love. I still listen to it quite a lot despite having played the games so many times.
Funny how Tims games always seemed to have a rather unique vision, including the music. Fallout, Arcanum (which is great also), Vampire (though I'm not a fan of the whole goth thing, it certainly fits in). ToEE is the most forgettable I suppose, but that Hommlet theme was absolutely beautiful and created a rather unique atmosphere.
I've grown a bit tired of the orchestral music often found in games nowadays, but I must admit that I would've been extremely interested in hearing the PS:T soundtrack with an orchestra mixed with the more electronic parts.
I really hope Mark Morgan gets back into game music at some point or another, he's truly one of the most underrated game composers I know of.
Also, for anyone liking his stuff, Obsidians NWN2 expansion called the Mask of the Betrayer is actually quite similar in many ways. Much more experimental than your standard RPG soundtrack, and quite varied as well. Best game soundtrack I've heard in a very long time.