I made an account just to make this review.
I really, really enjoy a lot about this game. The mechanics are solid, the stage design is also, for the most part, pretty good, and the bosses are also mostly good. I don't like the inclusion of Sonic 1 special stages, it doesn't help that somehow they're even more jank than in Sonic 1, and the Murky Mines and Talus Tempest bosses are just awful, frankly. Murky Mines I was constantly getting knocked off the edge of the fight, and Talus Tempest just doesn't have enough going for it. It's just a worse version of the Hyrdocity boss fight. The Bonus Stages also aren't designed very well IMO, especially the slot machine one.
But this game is killed by it's technical issues.
Whether it be standing on springs, clipping into walls, poor crushing detection, the multitude of issues that come from the Special Stages (Such as clipping out of bounds, spawning out of bounds, or failing as soon as you start the stage), or being unable to complete a level because you paused at the wrong time, this game is filled to the brim with technical issues that make it hard to enjoy.
To reiterate, I still think the mechanics are solid. I think the new shields are great, I think the shield combo system is great, I think most stages are designed well, I think the game looks incredible, the extras are all very nice, but this game is held together with duct tape and paper clips and that's its biggest problem.
Please, whenever you can, Fix these bugs and issues. They plague what I think is a fundamentally solid Sonic game.