As much as I say fuck Jim Sterling and everything he's about, he makes a great point that the Sonic franchise changes too frequently to build a staple for itself. Unleashed did something wonderful and created a 2D and 3D hybrid style that was universally fun. Then Colors and Generations improved upon it and were well received. No coincidence.

Just keep adding and improving, not starting over each time. I appreciate trying new things, but it seldom works for Sonic.

They already tried this with Sonic 4, and people hated it for some fucking reason.