You have no idea how close I came to buying the game off GOG.com just for the soundtrack. I already own the game for my N64, and I hear theres even more music in the PC version.
The Disco music, the Barn to be Wild level music...I just...man. Such great jams.
Reason I didnt/wont get it right now is that...the game just isnt good. Its not good...I'm willing to buy just the soundtrack from here, if I could.

I could never get the music working in my copy. It just refused to play, instead I heard all the terrible sound effects. You're right though, Earthworm Jim 3D is godawful.

I don't know about the N64 version and neither the PC, but the original EWJ 1 and 2 for 16 bits were composed by Tommy Tallarico (same composer for MDK, Advent Rising and much more games - president and founder of Video Games Live and Audio GANG). The soundtracks for EWJ are really awesome.

Oh man.
EWJ music. Simply the best. I've got good few songs of this game on my MP3 player. Nothing like rockin' to Falling or some soothing What the Heck? :)
Good thing I got this soundtrack in lossless format.