First time dabbling into 2D Sonic and the verdict is that I don't like it at all as a platformer. My distaste mostly stems from the archaic nature of the game's design and that is despite apparently being the most "polished" of the bunch? The whole selling point of the game is supposed to be speed but the amount of precision platforming needed goes contrary to the whole "gotta go fast" thing. Although precise platforming wouldn't be that big of a deal if the Sonic didn't control like he had soap tied underneath his sneakers. The insta deaths due to whacky collision detection led to nothing but annoyance and the dated save system where you get sent back to the very beginning of every single level is dumb and is an obvious attempt at padding out gameplay time. I mean even the mobile ports of the classic games let you continue from the specific acts so how come a more "polished" rendition of 2D Sonic can't respect the player's time? Now even when you actually manage to go fast it's during mechanical setpieces where the player takes the backseat and the level design basically plays the game for you, the result being the least engaging gameplay possible for a platformer. So, even the very idea of speed focused gameplay is detrimental to the final product. The lack of new content also gives it the impression of obvious nostalgia pandering since 70% of it is just borrowed stages from the classic games with a new coating of paint.
Music is the only thing about Sonic Mania I happened to like, so much to the point that I'd stop playing the game just to listen to the tracks on repeat. Though catchy music alone can't save a flawed game that somehow also struggles to have its own identity, it's like trying to apply bandaids on a bullet hole.