I sorta agree with most of what Crump said back there. Sonic 3&K had some fantastic levels and design that I just don't think Sonic CD could top. I felt some of the levels and bosses in the latter just felt too annoying to deal with. Time gates were a crazy cool concept, but they just didn't work out as well as I'd hope. You're way wrong about the music, though. Sonic CD's soundtrack was *crag*ing fantastic. S3&K had some great tracks, but CD edges it out.
http://www.youtube.com/watch?v=WrmD8hTAC7s