Sonic CD is brilliant and by far my favorite Sonic game. The aesthetic is the best in the series in my opinion, taking the abstract and neon nature of Sonic 1 to the extreme - Sonic 2 and on wards really changed the art direction towards things that were more grounded in comparison.
What makes Sonic CD so absolutely amazing to me is it's approach to Sonic design. Sonic 2 and Sonic 3 & Knuckles are built with a philosophy of layered, linear levels that are stacked one on top of each other, that periodically come together. The intersecting tubes of Chemical Plant zone basically epitomize the concept:
What this linear style enables is a system of beats where the level design will heavily encourage actions that will build momentum. Dips in the road that, if you're good, you'll realize that rolling into them will push you through the segment faster, or that barreling through a series of loops without interrupting your momentum will sling you up a ramp high enough to join a different path through the level. In fact that word "path" has become almost synonymous with great Sonic level design.
Sonic CD has no paths. It is completely free form. If Sonic 2 and 3 and Knuckles were obstacle courses, then Sonic CD is a skate park. This is reflected in the general shape of the stages - Sonic 2 and especially Sonic 3 and Knuckles have long, rectangular shaped stages with heavy emphasis on horizontal movement. Sonic CD's levels are enormous and tall and shaped like huge boxes. They don't contain paths but instead contain tons and tons of very unique objects, any of which you can trick off of in the same ways the paths in Sonic 2 onwards would force you to. By recognizing how the physics work for the series, Sonic CD becomes this amazing experience that feels more like parkour than anything else. When you play Sonic CD correctly, you glide through the stages, both horizontally and vertically, with absolute ease.
This added emphasis on vertical ability is reflected in the only real changes Sonic CD makes to the Sonic engine. All the Sonic games are built off of the same engine, but each game makes small tweaks along the way. Sonic 2 and Sonic 3 & Knuckles tweak the engine in iterative, progressive ways, but Sonic CD mainly sticks to the engine as Sonic 1 saw it except with regards to how it considers air movement. Sonic CD changes the way you build momentum in the air and how your momentum is stored in the air that lets you accelerate mid-are in pretty much the same way you do on the ground. This has the effect of making you feel like you are running (or rolling, thus breaking the speed cap) mid-air rather than jumping.
A lot of the complaints about Sonic CD, I flat out do not get. The sign posts, as an example. I don't understand how people can't control the ability to change time zones at will. It's pretty easy to force your time post to disappear once you grab one, and you should be able to control your speed well enough to basically get to decide when and where you want to go in the game. The multiple time periods are really what make Sonic CD so great - these huge zones are multiplied by four. I don't think some of the detractors ever actually sat down and explored these zones.
And exploration is why you play Sonic CD. Not to race to the end of the stage. You play it because you love the Sonic physics and want to try out all these unique obstacles Sonic CD has to let you further play with the physics. Sonic CD has a lot of platforms and obstacles that challenge your mastery of Sonic's physics in ways no other game in the series does. When you play Sonic CD right, it looks sublime.
This is what Sonic CD looks like when you play it correctly
Constantly moving, with ease, in virtually every direction. It's like one long combo, you never stop interacting with things. Playing like that is actually pretty challenging, and the free form nature of the acts means it's very easy to basically "groove" in the game and just make up your own routes. I love Sonic CD because, even after decades of playing, no two playthroughs are the same for me. I still constantly find new ways to tackle the levels, because the ways you can get through them are basically infinite.
I think the claims about narrative surrounding the game are weak deflections from detractors. My opinion wasn't made because the game was "rare" (it wasn't rare, by the way). I played all the Sonic games in order as they released. Sonic CD blew me away the day I got it. It epitomizes everything right about "CD games" and what they were supposed to bring to the table. It was everything I liked about the series before, but just way, way, way more. Like what I liked before, but to the nth degree. I feel the exact same way about Rondo of Blood. I felt like Sonic CD was an enormous improvement over Sonic 2 and, at the time, I felt like it was more in line with Sonic 1, which is the game I had played much more at the time. I remember actually being
extremely disappointed with Sonic 3 because it
wasn't like Sonic CD. Sonic & Knuckles is what ultimately brought me around on Sonic 3. Playing up admiration of Sonic CD like it's some sort of badge of pride is lame. I could just as easily accuse detractors of being blind as to the obvious reason why they can't breeze through a Sonic title they've played only recently and a handful of times like they can the classics they've played thousands of times over the decades. You may have forgotten it, but part of the joy in Sonic games is that "just one more time" mentality. They're designed almost like arcade titles.
I will forever love Sonic CD. I actually prefer the Sega CD original over Tax's port (although I love Tax's port) because Tax's port has a few physics and timing changes that only extremely hardcore people notice that changes my playstyle enough to annoy me. I've seen people wish for an open world, free form sonic game before on these and other forums. Sonic CD is basically that.
