I only did one music pack years ago, for a beta version of the vampire blood chronicles mod (now stuck in limbo) but it wasn't that hard, but I have to agree the ambience music should be fitting for that area or scene, where as action music is needed for firefights say, and something epic for a boss battle, even the super star wars games on SNES had the same overture from the movies, cept battles had some thumping 16-bit music to accompany them, but I suppose at the time the game might have had development limitations, but it doesn't stop us as modders from expanding on these ideas