Well, the game isn't even really 3D, but it's a very clever pixel trick. Most Sonic fans don't like this game but I actually really enjoyed it.
PlotSo we know in the classic games, Robotnik converts animals into robots, well in this game he uses these little birds who Sonic is friends with. Sonic has to save all the little birds by destroying the robots. The birds then follow Sonic around in a trail (kind of like Snake) until the end of the level.
GameplayThe slippery controls take some getting used to, but it's pretty good and you can't fall off any ledges, though there are a lot of spikes to watch out for. There is spikes galore in this game! One bad thing about it is that when you get hurt all the birds start flying around everywhere and you have to collect them all again. It's especially frustrating when the birds start flying over spikes and it adds a bit more of a challenge that the rest of the game lacks.
Although the game is pretty easy, one slip up can send you sprawling back to the last checkpoint.
Overall, I really liked the game. The last I played it was two years ago or something, but I still remember it really clearly and I had a lot of fun beating it.