Sonic CD is a bit of an oddball as far as the early main-series Sonic titles go. It had a lot of different ideas that were not really explored again and Yuji Naka had very little involvement with the game at all. With a much greater emphasis on exploration as opposed to speed, it doesn’t quite fit in with the other games in the series, yet it is definitely Sonic.
The soundtrack of this game is well-known because they changed it for the US release. Both soundtracks have their merits, but …