Looks like it's time for a Sonic 3 w/ Sonic and Knuckles style game. New worlds, no new Characters... Sonic, Tails, and Knuckles. That's it. Sonic 4 looked like Sonics 1&2 in HD... Nothing new, just a rehash. Just go 2D with new places to see. Not a hard formula.
Ask stefl1504 for a sig, even if you don't need one.