I humbly highly disagree with you Plant. It’s a great game. I think the mechanics are great fun. It’s way, way better than Forces.
Have you finished the game yet?
The stages start off decent, but they gradually get worse.
The longer you play the game, the more it shows its ugly head as an obvious fan project. There are tons of classic Sonic game stage assets, but they're thrown together to make these Sonic Mania stages. If SEGA made a "Sonic Maker" game, Sonic Mania would feel like a run-of-the-mill offering. The final stage is an absolute trudge, since it is so long, riddled with checkpoint after checkpoint, when all you want to see is the fuckin finish line.
Sonic Mania shines the brightest when it's being original... which is unfortunately rarely the case. So what is this? Above all, if say it's the bonus stage where you try to snag the chaos emeralds. However, once it's over, you have to try and find another one of those giant rings for another chance. Finding them in itself is a pain in the ass because the stages are so fuckin big. But even when you do, you're unlikely to be successful, because the chances to try this bonus stage are so few and far in between, and your prompt failure gives you little chance to practice and get better at its unique controls.
What else is original? The bosses. But while they're original, they feel out of place and overly aggressive by classic Sonic standards. You can count on losing your collection of coins every fucking time you fight a boss.
But yeah, Sonic Forces had its own rough spots, but I'd say that's a much better game. It took me a bit to get into it, but I really enjoyed it and happily went above and beyond to 100% Forces with all Trophies for the main have and Shadow DLC.