When I first saw Sonic CD on the Gems Collection, I honestly thought I was going to hate the game, as I have played some of the other Sonic games to me having mixed or pure hate for the games. Fortunately, Sonic CD wasn't one of them. I actually like this game a lot because of the platforming is as precise as the other Sonic games like Sonic 3 and Knuckles and Sonic 1. The story takes place when Sonic has to save a world called Little Planet from Eggman. After completing Palmtree Panic Zone you find out that another character has appeared. She goes by the name Amy Rose. She gets kidnapped by a metallic robot version of Sonic called Metal Sonic.
The gameplay is at it's finest with the high speeds, the precise platforming sections, the music in some sections and the switching between the past and present make this game a unique Sonic game and an awesome one as well. Some say that the controls were crap on the Special Stages but surprisingly, I had little to no problems with the special stages.
The only problems I had with the game was the emulation problems that Sega left out which include glitches, poor music porting, the time warping scene being weird and the lag between finishing an act and starting the next one. But then again, I did not expect Sega to do a good job at porting looking at their track record with ports/remakes, but I digress...
This game overall is a fantastic Sonic game which is available for a number of consoles.