Sonic the Hedgehog is chasing Metal Sonic, who kidnapped a girl named Amy Rose. It turns out that Amy had used the tarot cards to find Sonic, but was kidnapped in front of his very eyes. Sonic has to get the Time Stones and to travel through time to foil Doctor Robotnik's (Doctor Eggman in the Japanese version) latest plot.
The game's key element was the manner in which the player could travel to 4 different versions of each level in 3 different time periods. This was accomplished by speed posts scattered around the level, saying "Past", and "Future". There were never "Past" signs in the Past and never "Future" signs in the Future. If you defeated all the enemies in the past, then you traveled to the future it would be the different "Good Future". You would receive the good ending to the game by completing all the good futures or by collecting the 7 Time Stones in the Special Stages.
The game itself has Sonic feeling heavier than normal. The spin dash he does is weak, but he compensates with the Super Peelout. The Super Peelout, performed in a manner much the reverse of the spin dash, by pressing up and a button, causes Sonic to rev in position until you release the button, at which point he speeds off.
Both the Japanese and American versions of Sonic CD had their own soundtrack. Different people have different tastes about the music. The US version also replaced Amy Rose's name in the manual with that of Princess Sally to garner support for the television show, despite the fact that the Princess Sally character was already established.
Here is a list of rounds:
Among the most noteworthy changes of this version was the fact that the entire FMV Anime intro and ending sequence is available for this version. The Mega-CD version only had part of the intro and ending sequence. The Japanese version of the game had its manual translated from the US version.