I do have a soft spot for CD. Most people who have played it think it's garbage, but I actually think it's alright overall, but it does have issues holding it back. Namely, time traveling and going after the Metal Sonic capsules is tedious and goes against the "go fast" nature of classic Sonic, rings still exist in time periods they shouldn't, resulting in weird out of bounds rings being on screen, and the bosses are kind of a joke. Palmtree Panic's boss is far too easy, Collision Chaos's boss is just a tedious pinball section with the goal of reaching the top, etc.
Ignoring the time travel and just playing it like the other games without caring about which ending I get however, I do find the game to be alright. Both of the OST's are pretty good with a few outright bangers here and there, some of the levels are particularly pretty to look at, and although most of the bosses are pretty garbage I do enjoy Metal Sonic and the final boss even though their difficulty feels swapped and they probably should have saved Metal Sonic for the end of the game.
Um,have you ever "seen" how the cutscenes in Sonic CD really looked?
Just imagine if the game would look like this,but extremely laggy. Overall, Sonic CD aint that bad,but its not all that good in general.