Just a few more improvements and it'd be perfect
This is very well done overall, looks good, works well. There are just some areas that could use some improvement:
Physics are slightly awkward. Getting over what should be a simple wall or short jumpable cliff can be tricky, for some reason sonic can get stuck as he reaches the top and doesn't get up onto the next platform, instead just falls back down. This seems to happen very often.
Enemnies can hurt sonic while preparing a spin dash and coming into contact, in the official games it's the enemies that get hurt when this happens.
There needs to be a WASD option I think. Some poeple prefer the arrows, some prefer to direct with their left hand. I know when I play offocial sonic on the emulator using WASD makes a world of a difference. My friend on the other hand can't stand it. An option to choose at least would help.
But for the most part it's very good. Only needs a little bit of improvement. And that's just if you're fussy like me. :)