Played Sonic Mania for the Switch.
On the good side most of the devas made fan versions of the original Genesis games so they loved what you loved. The game plays sort of like Sonic 3 & Knuckles, new Sonic 3 sphere planets have been added and they take the place of lamppost bonus stages allowing you to earn tokens to unlock new gameplay options. Several old stages appear with some minor twists that make them a little more enjoyable. New stages like Metallic Madness offer up some cool things like background/foreground swapping and shrink rays. Old enemies appear as well as all kinds of shoutouts to past Sonic titles. And while it repeats a bunch, it also introduces several new stages and enemies. Overall, if you liked Sonic 3 & Knuckles, you'll probably tolerate Mania.
On the bad side most of the devas made unstable fan version copies of the original Genesis games so it's buggy as f**k and prone to crashing even after patches. The game plays like the worst combination of Sonic 1/2/3, like no Hyper mode, terrible minigames, no goal of having smooth effects, reeks of people trying to do to much with rough cut leather stitching it together. Lamppost minigames are the boring sphere planets which offer nothing in game unlike the gumball, slot, or fun gravity pinball games from S&K3. Unlocks apply to no-save files only so if you want to play "Knuckles & Knuckles" in Lava Reef you'd better turn on Debug Mode to drop goal posts because you need to beat 18 stages and deal with one very long intro first. Several old stages appear, couple of the new ones suck or seem empty (stardust speedway). Lots of shout outs to stuff you will never care about. New Chaos Emerald minigame is the worst of 3D Sonic games: A 3D raceway specifically reduced to a horrible dot matrix level of quality display with poor controls. And it can't make up it's mind on what to flatten out like holes in the ground or bumpers vs edges or bumpers in the middle of the damn road, or what to raise up like spikes of doom or pillars you can run harmlessly through. If you liked Sonic 3 & Knuckles, you should probably just get the Steam version of Mania ten years from now through Piratebay (no spyware DRMs that way) and grab a hack for it so you can play as Knuckles & Tails with Level Select or a combination Sonic that has his instant shield, figure eight dash, and only-works-half-the-time air spindash.
Score: 6/10 or about six points higher than the average of Sonic games currently but still several points lower than the Genesis games.