Well, no Sonic game can ever surpass S3&K.
However, Sonic Mania's quality is certainly high up, in terms of level design. It's fantastic.
A surprising amount of people hate Blue Spheres for some reason, but I always liked it. That being said, they were a little too monotonous in Mania, and should have been divided with gambling bonus stages or maybe something new entirely.
This pretty much mirrors my thoughts.
Yeah, since I missed the Mania discussion, may as well leave my two cents now:
-Ruby Delusions is like sex for my ears. It's my new favorite Act 2 boss theme for the series, even if S&K still has the best Act 1.
-Love the course selection. Hydro City, Flying Battery, and Lava Reef more or less represent the best of S3&K (I do miss Sky Sanctuary, though).
-Glad that Blue Sphere progress is cumulative across all save files.
-Knuckles still has unique paths, so that's cool.
-Oil Ocean Act 2 boss, that thing just throws the kitchen sink at you, and I love it.
-TAILS CAN USE CHAOS EMERALDS
[spoiler]-The Mean Bean Machine and the Amy dolls were both ingenious and had me laughing maniacally.[/spoiler]
So was it perfect? Nah, of course not. But it's damn good, the next best thing after S3&K easily. My nitpicky complaints are as follows:
-The "pinch of death" where two vertically moving platforms slide past each other, and you're standing at the edge of the lower one, you die from the top one coming down rather than get pushed aside. I know that's true to the Genesis physics, but I think there is such a thing as being too authentic.
-I need to test this more, but in co-op it feels like the computer tries to take back control of Tails EVERY SINGLE TIME he goes off-screen. Which, this is a Sonic game, that happens a lot. It seems to ignore Player 2 control inputs that were entered before Tails actually lands (IE, if you're holding the control stick while he flies in thinking you need to get him running right away, the game ignores you and leaves Tails under CPU control until you enter a new input).
-Blue Sphere does break the flow of the game after a while, especially on ye olde Super replays. Compounding this is that they as bonus levels do not give any normal-stage-relevant bonuses, like rings and shields. Since its score is cumulative across all files anyway I'd have appreciated an option to just play it separately after the game was cleared.
-The 3D special stages use flat ground textures for the bumpers...WHY?! Also having both bombs and spikes is redundant since they are both the same thing functionally yet look completely different and are thus easy to miss at high speeds if you're looking for one and get zonked by the other. Overall it's just harder to tell what's going on in the stages than it should be. They also control like the Pilotwings Rocket Belt, but as a gaming veteran I can dig the "bad but in an oldschool nostalgic bad kind of way" design choice.
-Hydro City Act 1 is the one stage that feels inferior to its original (oddly, this is the one time when Act 1 is the heavier remix than Act 2). The boats and bubbles just break the flow of the stage.
-Unpopular opinion, but think Press Garden is the weakest zone. I like the stage gimmicks, but the color palette is horrid. In Act 2 there are background pillars using foreground color palettes, which is a completely amateur mistake that makes the zone feel unprofessional. Ditto for the tree trunks using the background palette, though that's not as bad since at least they're noticeably larger than anything in the background. I also think they could have made better choices for the Act 1 crates, two shades of blue to differentiate between background and foreground is not as clear as it should be, I'd have rather seen the "solid" color used for standard crates and a grey metal/stone palette for the tougher ones, which would have made the Act 1 boss more intuitive. I also think that the Act 2 boss was an unnecessary difficulty spike.
-On Nintendo Switch there is a bug that lags the UI tremendously. The Home button takes an eternity to respond, and if you hold it for the Quick Sleep, the menu will pop up but will not respond to control inputs. I have no clue how that could possibly have been missed in play testing, and Sega needs to patch it, pronto.