The game has the same plot as the 16-bit version; an evil scientist named Dr. Robotnik (known nowadays as Dr. Eggman) had captured all the animals of South Island and transformed them into robots. Sonic - the hedgehog controlled by the player - must progress through the six zones of South Island to rescue the animals and restore them to their natural form, and defeat Dr. Robotnik for good in the end.
There are six Chaos Emeralds that can be found in each zone. Whilst collecting them are not mandatory, if all six of them have been collected after Dr. Robotnik is defeated in the final zone they will provide an alternate, good ending.
The game is pretty much identical to the original Sonic the Hedgehog; the game consists of six zones that Sonic must travel through to the end of each level and save animals from Dr. Robotnik. The game also retains all the actions and features from the original 16-bit version, such as being able to attack enemies by jumping on them or rolling, etc and being able to collect rings which can partially protect Sonic.
However the game does contain some minor differences; the Chaos Emeralds that Sonic could collect (though not strictly required) can be found in one of the acts in each zone instead of being located in a special stage. Collecting all the Chaos Emeralds will grant you a good ending after Dr. Robotnik is beaten.
A prototype of this game was featured on the popular Nickelodeon game show Nick Arcade.