Next thing I want from a 3D Sonic game, MULTIPLE CHARACTERS. They don’t have to have unique stories or super different gameplay styles, just make them variations of Sonic with different abilities. The way the 2D games do.
Do Sonic, Tales, Knuckles, Mighty, and Ray the way ma is did them. Have the Chaotix play the way they do in Knuckles Chaotix. Have Amy and Cream play the way they do in Advance. Do Blaze the way the Rush games do. Figure out how to do Team Dark and Silver. Just go nuts. It would add in TONNES of replayability, especially if you have to unlock the other characters in interesting ways.