Sonic CD is one of the most mis-understood games, it seems.
The graphics look beautiful.
The music is excellent.
The gameplay is spot on.
One common misconception that is often raised is the level design.
Yes they are large; and hard to navigate (at first), but that is the point.
Sonic CD remained true to Yuji Naka's original design of having the most basic control scheme possible for a platformer: Run, and Jump = a "one button" game as he originally intended. (edit: there is quite useful speed boost in Sonic CD - misunderstood Skykids statement and confused myself
)
The "point" of the game requires that you go back in time to destroy Robotnic's pollution machine or whatever it is, so the future will be bright and cheerful.
Sonic CD is about exploration. You aren't going to just push right, and jump to avoid obstacles.
Now, as you explore the levels, it is first necessary to locate the "Past" signposts, and then figure out a way to build up and maintain enough speed to warp into the past. Very often if you choose your path poorly, Sonic will cross a "Future" signpost just as he is fast enough to warp, and will "accidentally" warp to the Future. This was clearly designed to thwart careless and inexperienced players.
Every (iirc) level has one key "give-away" location where it is guaranteed to warp to the past. For instance, on one of the conveyor belt levels you will find a "Past" signpost near a vertical conveyor "tunnel". Hit the switch so the conveyor is running "up" and then when Sonic jumps in he will be spun and juggled by the conveyor belt allowing him to warp without error. Other levels typically have a "Past" sign post near two opposing spring-bumpers. Get between the two bumpers and Sonic will be ricocheted until he warps. As a beginner playing the game most people try to find a straight-away and gather speed by running, this is where the design is brilliant, and you will be thwarted.
Further genius in the level design is apparent in the way the levels are re-mixed between the Past, Present, and Future versions. People have actually argued that these are haphazard careless placements of the platforms and corridors, but those are the people trying to run left to right without learning to explore.
Every level can be speed run, though, once you are experienced enough. Sonic CD includes a Time Attack mode, and it was by completing all of these levels with incredibly low times that further bonuses and extras were unlocked on the game. It takes a lot of practice to find the routes to run most directly from beginning to end of a level, but they
are there. Once those routes were learned, they could be applied to the game when playing a complete play through, and by that time you will realize why Sonic CD is the best Sonic game ever created.
To reiterate:
The levels are not haphazard, people's playing skills and expectation were.
Also, can't imagine where Skykid got "stuck" in the background, I've never heard or known of anyone to get stuck by a glitch in the game.
I would have loved to see a comprehensive guide book of this game, I have asked my typical sources in Japan, but no-one has ever seen one. There were some mini-guide supplements that came with Beep! or some other mag, but none that covered everything in the game. There are so many little secrets and nuances.
After countless playthroughs, I recently stumbled upon a hidden chamber underwater that contained a statue (like a goddess or sea maiden), when touched she started spewing rings - I was delighted! the game continues to offer surprises over a decade after its release.
(just kidding 
)
