I've got three songs from Incompetech randomly spinning with eight different sets of sound effects playing over them (also random). I'm finding it an incredibly rich/dense/vibrant soundscape.
You can play the game, too, but you don't have to, really. ;)
(for those who played the beta version a year or two ago--the comments were much appreciated; I'm sorry I didn't manage to work more of them into this version, but I needed to just let go of it, move on...and hopefully the sounds/music make a huge difference) :)