Sonic CD is a colorful, lush game with two great soundtracks, and some creative boss battles.
That being said, its levels are complicated pains in the ass, lacking any of the streamlined stage design of the Genesis titles, and completely counterintuitive to either finding the special stages or going back in time to make a good future. A high percentage of the play time feels like a series of amateur Super Mario Maker levels by someone who felt you can't have enough platforms, spikes, and conveyor belts.