My thoughts on fixing Sonic

The Sonic franchise is having a hard time staying relevant in these times, So anyway, here are my thoughts on how we can fix the series.
The first thing I want to discuss is the transition to 3d. Now I know, the transition to 3d had an effect on everybody, even Mario. But what made Super Mario 64 work so well and not Sonic Adventure. Now don't get me wrong, I think Sonic Adventure is a great game, but it certainly didn't do everything right. What made Super Mario 64 work was most likely how they kept with the old formula, but since what works in 2d doesn't always work in 3d, they made a few changes. For instance, they added a health meter and instead of having a map like in Super Mario World or Super Mario Bros. 3, they had a hub world, peaches castle, but other then the few differences, it still basically uses the same formula as all other 2d Mario games. Sega did a good job at sticking with the old formula in the first Sonic Adventure, but the sequel didn't do as well. For instance, how far off the settings are from other previous games. In the Genesis games, you are in fictional areas that are bright and colorful, but now we're in a city. Now I have nothing wrong with changes from one game to another, as a matter of fact, you have to have changes so that you're series doesn't get boring because of the same old thing over and over again. Super Mario does that well, for instance, in the first Super Mario, you have a basic platformer, in the third one, they add a tanooki suit and can hold shells, in Super Mario World they added Yoshi. See how they change one thing at a time instead of making a whole different kind of game each time? This is most likely why it's super hard to please the Sonic fanbase, because you have a whole group of people who came from different games in the series, for instance, one person might have became a fan from Sonic Adventure 2, so they like the Story and the Human interaction, while as I came from the Genesis games and like the Gameplay and lack of story, so you have a pretty divided fanbase. And Mario on the other hand, has had basically the same formula for over 30 years, and so his fanbase all have basically the same opinions. Basically what I'm trying to say is that Sonic needs a brand identity, because his series is all over the place. Of course, it's probably too late now because making one decision will kill off one part of your fanbase and making the other decision will kill off the other part of your fanbase. Anyway, if you disagree with me, I'd like to here your thoughts, so feel free to reply.