Some of it seems 'meh' but some, like the invincability jingle, aren't too bad. The final boss theme had me thinking it was going to be the same one from Sonic 3 because the first few seconds sound like it, then I realised it was a totally new peice of music. Maybe it'll seem better once I actually hear it during the game.
Edit: It's sounding a little better now that I'm listening to it long enough to make a better judgement. Not bad.