i don't anyone bringing the complete OST stateside, given that it's two discs. If i remember correctly, the Ocarina of Time OST was two discs, but the US soundtrack was only one.
i've heard many songs from videos and MP3s, and i'd have to say the OST is probably worth the purchase.
Rory C: If you want Metroid Prime music, check Kazaa. Someone recorded most if not all of the music from the game. Sound quality could be better, but it'll do until they release an actual soundtrack, *if* they ever do.