Ok so I stumbled with this fangame while navigating twitter and I wanted to comment about what I played so far.
After two stages, I have to say the game is nostalgic. It embodies the soul of classic 2D games and have translated the 3D blast levels amazingly. I enjoyed running around Green Grove and Rusty Ruin (even though there was times i couldn't walk for 5m before getting hit by a badnik or a trap), and i must kudos how you translated the infamous slope with trampolines. It gives the same vibes as the ones i got in Blast!
I have no complain for the bosses either for now. They are meant to get away with one live or two while figuring the pattern.
The special stages, though...
Look, I know they are meant to be a challenge. The Super Sonic gameplay and extras are a reward after all, and they must taste like one. But my feeling while playing them... there is a spanish word for that feeling: encabronado (which mean a combination of angry and frustrated).
Even with the tips provided on the comments (and yes I read the comments before starting to write) they become such a pain which leaves a feel of unfairness. Even the difficulty curve seems created to make you mad. In official Sonic games the 3 first emeralds can be obtainable in the first or second try of the very first run. I think these kind of level must feel like they are doable, to make you think "oh shoot i was so close i'm sure next time i will get the emerald", and that was not the case.
All in all, i'm decided to go forward and rediscover the stages and bosses within the game and i'll be waiting for any updates or new projects. Keep that work up!
-EDIT- the second special stage can be done in second try. Yes tips help, but still, just half more second of anticipation would be really useful