This fangame has some serious design issues which make the game itself significantly more frustrating to play.
1. The graphics are great, but the camera is WAY too zoomed in! I thought that the game would take advantage of the fact that it's widescreen, but the camera is so zoomed in that it makes the game disorienting and there's not enough time to react to anything. The camera should be more like Sonic Mania or any of Christian Whitehead's remakes. Instead, it ends up being like Sonic 4's.
2. The level design needs a lot more work. The enemy placement just isn't good, and I kept running into badniks that were almost impossible to avoid. The way that the levels are stacked makes the player repeat long segments of it if they miss a single jump. This makes the levels very repetitive and long.
3. The physics don't feel right. There's not enough momentum, Super Sonic doesn't have any special abilities, and the super peel out is practically useless because of how long it takes to charge. On the other hand, the spindash is overpowered. Also, some of the music is wrong, like how the invincibility music is from S&K, not 3dB.
4. The way special stages are handled is by far the worst part of the game! I never liked the giant rings because you shouldn't have to slow down and explore a level in a Sonic game. That's why Shadow the Hedgehog got so much criticism. The special stages themselves have even more issues. The controls are WAY too slippery to even be remotely manageable, and the reaction time is horrible due to the speed and very short render distance of the rings and bombs. These special stages are nearly impossible to beat. The bridge stages from the original 3d Blast are way better and I'm surprised that you didn't use those. The half-pipe is far too overused anyway, and this is an opportunity to come up with something new.
Overall, this game is very flawed in terms of design. And this is coming from someone who's completed almost every Sonic game! I see a lot of potential here, but for now, I'd rather play the original 3d Blast.