Not as good as 2 IMO, but a good Sonic game nontheless
The single player is pretty good. The levels are nicely designed, and are improvements of Sonic 2 Levels. One of my complaints is the Carnival Zone. I have yet in 8 years to finish Act 2. I hit a dead end, and can go no further. It's very frustrating and I refuse to look at a guide. My other complaint is the fact that it seems a bit slower than Sonic 2 was. Sonic 2 I could breeze through Acts in 2 minutes. (48 seconds for the first Act) but here the levels are more platform than speed. Sonic is about Speed not platforming (See all 3-D Sonic Games).
While not as good as Sonic 2 it's still 3rd on my list of top Sonic games. I grew up with the Genesis Sonic games and still go back to play them to this day. As for this game the Carnival Zone will forever haunt me and I will always get faster times for time attack.