Sonic the Hedgehog CD was released in 1993 for the Sega CD. 
It was developed and distributed by Sega. It is a
side-scrolling action game like most of the other Sonic
games, it contains some of the fastest, and most engrossing
gameplay ever. Your goal in the game is to defeat Dr. 
Robotnik, not only because he turned your animal friends
into robots (for the 3 millionth time) he has also kidnapped
Amy Rose, Sonic's girlfriend (I think she is anyway, dang
the game's ambiguous storyline.) 

Graphics-10/10- The characters are all quite large. Each
features fluid animation. The character designs continue the
Sonic legacy, they are very creative. The backgrounds are
very original and are quite detailed. The game-opening
animated cinema is excellent, the quality is second to none
and it really helps set the tone for the rest of the game. 
Overall, the graphics are excellent, the game features
imaginative characters with superb animation. 

Pros- Excellent character design. Large characters. Very
colorful levels. Well-done animated cinemas. 
Cons- None that I can think of. 

Sound-8/10- The music is another great feature in this game,
it is very well done. It's not as good as the import
version's, or the original Sonic the Hedgehog, but it's
still good. The music fits the themes of the levels
perfectly. The sound effects are great, they are clear as
could be and fit each action perfectly. 

Pros- Excellent music that truly added to the experience of
playing the game. Great sound effects. 
Cons- As good as it is, the music isn't as good as the
import version's. 

Gameplay-10/10- Your universal goal in each of the game's 
levels is to free your friends, who have been trapped in
metal containers at the end of an Act. There are 3 Acts in
each level, the third Act is the Boss Act, the Boss for that
level is at the end of the level. All of the levels have
different settings, they are all very unique, and they are
well laid out and are quite diverse in style. A new
time-based element was added to Sonic CD, you can play a
level in the Past, Present, or Future if you hit a marker
with the time name on it, the levels design is identical in
each, the time element does add different enemies and
changes the look of the level to correspond with the time
zone. This is a very welcome addition to the series, it
helps to keep the game fresh. 

Pros- Classic gameplay that never gets old. 
Cons- None that I can think of. 

Control-10/10- You can do a plethora of things in this game
to defeat your foes; the two main ones are, jumping on them
or spinning through them. A new spinning attack was added to
Sonic's repertoire, it is very well done. 

Pros- Very responsive. Simple controls. 
Cons- None that I can think of. 

Presentation-10/10- Everything fits the game's theme
perfectly. The character design are among the best ever in video games. 

Pros- Fits the game's theme perfectly. 
Cons- None that I can think of. 

Challenge-9/10- The game's challenge progresses gradually as
you get through the game, much like all of the other Sonic
games. For the most part, it's not too difficult, with the
exception of the last few levels. 

Replay Value-10/10- It's a timeless Sega CD classic that
you'll want to play for years to come, if you can find it. 

Pros- Excellent gameplay makes it a game that you can play
for years to come and never get bored. 
Cons- None that I can think of. 

Overall-10/10- This is undoubtedly the best Sonic the
Hedgehog game ever. The graphics are unparalelled on the
Sega CD, or any other platform for that matter. It stands
the test of time better than most games. Even after seven
years, the game still seems new and refreshing. It added
quite a few new features to the series. This game stands
tall as one of the few bright spots in the Sega CD library. 

Final Thought- This game is a true classic. If you're  a fan
of any of the Sonic the Hedgehog games, buy this game,
you'll never regret it. The gameplay is top-notch, as is
virtually every other aspect of the game. The time travel
element adds a nice twist and increases the game's longevity
in my opinion. This is the Sega CD's finest game in my
opinion, it does so many things well, it's not even funny. 
It's one of the few Sega CD games that is worth the purchase
of the system.