The thing about basically every Sonic game since the Dreamcast days is that if they hadn't featured Sonic, nobody would have bothered to play them and we wouldn't still be talking about them today. Even the better ones are fairly average compared to other contemporary games. The Sonic brand clearly still has selling power, but the games themselves have been very unremarkable and forgettable at best.
The 16-bit 2D Sonic games on the other hand, and Sonic Mania by extension, are beloved because they are actually very good games. Even if they hadn't featured Sonic, we would still be praising them and playing them. The tightness of the controls, the fluidity of the graphics, the colorful art style and the catchiness of the music all combine to make a series of highly memorable games.
It's not faint praise or nostalgia what's at play here, it's the simple difference between what makes a great game and what makes an average game. The fact that the Sonic brand is attached to all of these games is what tends to cloud our sight and make it difficult to see the difference between the two.
