Sonic CD was Sonic's first and only foray onto Sega's CD add-on for the Genesis. The game takes place after the events of the original Sonic the Hedgehog game, and introduced Amy Rose and Metal Sonic to the Sonic universe. As most people have probably played a side scrolling Sonic game before, I will just skip to the important aspects of this release.
Sonic CD is a gorgeous game. While it technically limited to the same 512 color pallette, and displaying only 64 colors at a time, it somehow manages to look and feel a lot more colorful than the cartridge games. The background are a lot more detailed, and overall everything thing looks sharper and more polished than Sonic 1 and 2.
Unfortunately, there is some slowdown in this game. Every time you lose a large amount of rings, or there are a handful of enemies on the screen, the action slows to a crawl. While brief when it happens, it cuts into the action and should have been avoided.
Sonic CD's soundtrack was completely changed for the American release of the game, to the dismay of the gaming press at the time. I am not going to debate whether it was a smart move or an improvement as it does not really matter. The soundtrack is excellent. The opening song for the first stage, Palm Tree Panic, is especially good. Throughout Sonic CD it is obvious a lot of attention was paid to the music, assuring gamers were getting more than a Genesis (or Super Nintendo) cartridge could offer. The energy was well spent. As a bonus, the music is encoded as red book audio and can be played on any CD player.
The gimmick in Sonic CD is the ability to travel through time. Scattered about the zones are "Future" and "Past" sign posts. Once you build up enough speed for a period of time, you will travel back or forward in time, depending on the last sign post you past. The past and future versions of the zones feature new music, and a new color palette. There are also some item and minor level changes as well.
There are 7 zones in total. Palm Tree Panic zone is the typical opening Sonic zone, featuring lots of trees and other greenery. Collision Chaos Zone is a weird pinball like zone featuring a lot of pink. Tidal Tempest Zone is the usual Sonic water zone. Quartz Quadrant is a quartz mine. Wacky Workbench zone is a large factory. When you touch the floor, you go flying to the top of the level. This is a unique zone in that it relies on timing and precise jumping, rather than speed. Stardust Speedway is a futuristic city. Metalic Madness is Eggman's base/factory/city and the final zone of the game. Each Zone features 3 acts, following in line with the original Sonic the Hedgehog game. The third act is a boss fight with Eggman. There are 21 acts in all, not including the various time periods you can travel to.
With the exception of Wacky Workbench, the levels flow well, allowing Sonic to zip through at top speed. However, to truly beat the game, and see the proper ending, you need to spend some time exploring. First, you need to travel to the past. From there, you need to find and destroy "Eggman's Machine" which will unlock an alternative (good) future in the act. If you go to the past and destroy this machine in the first 2 acts, the third act will always be the good future. The good future shows what the world would like if Eggman was detroyed. This offers a lot of replay value and adds some adventure aspects to the game.
If you don't want to spend all of your time traveling through time searching for Eggman's machines, you can also collect the 7 time stones in the bonus stage. If you have collected 50 rings, you will have the opportunity to play a bonus stage at the end of each act to try and collect these stones. The bonus stages are a Mode 7-esque arena where you must destroy 6 UFOs in the specified time limit. The stages aren't as smooth as games like Mario Kart on the Super Nintendo, but do a good job showcasing the extra power of the Sega CD.
The boss battles feature Eggman in various robots just like in previous Sonic games. His machines are a lot bigger and more detailed in this game. On the whole, Sonic CD is not that difficult and experienced gamers should be able to breeze through the game.
Sonic CD introduces a peel-out maneuver that exclusive to this game. While standing still, hold up, then press the action button to charge up. Release up and Sonic races along at top speed. What is unique is that he is not in his usual "ball" form and is susceptible to enemies. The tradition spin dash is also features, but is not as fast.
The game features some nice FMV sequences and the beginning and end of the game. It is not intrusive like other games of the era, and the animation looks terrific. The videos were obviously designed around the limited color pallette, and are not grainy or blurry in the slightest.
Sonic CD is a great Sonic game and is a must have for Sega CD owners. The control is every bit as responsive as a Sonic game should be. The graphics and sound are top notch, and have a unique futuristic techno feel not seen in the cartridge releases of Sonic. You can whiz through the levels or take your time and explore, destroying Eggman's Machines and seeing the alternative futures. The excellent CD soundtrack and fun bonus stages are the icing on the cake. I highly recommend tracking this down.
Graphics - 9/10 Absolutely stunning, but hampered by some slowdown
Sound - 9/10 Brilliant soundtrack
Game play - 8/10 Classic Sonic game play
Overall - 8/10 This is a great game, and a must own for Sonic fans