I finally got to sit down and play Sonic Mania (Plus) after much contemplation. Now that I have completed Sonic's story, and have an informed opinion on the game, my stance still has not changed. The game is everything I anticipated/feared it would be: A big (unnecessary) nostalgia knobjob to that part of the fanbase that won't shut up about wanting another classic game.
With that said, until I can play Sonic Forces to "complete the set", I don't think it's a "bad" game by any means. But I DO believe it is overpraised/overrated, especially for being a game that's 75% recycled from the games of the past.