Nothing. I don't think they have a clear conception of what they want to do with a 3D Sonic.
I see something like Mario 64, and how it was basically a design doc for how Mario (and similar characters) would be defined in 3D. Sure, they've added and removed things along the way, but there's a core there that figured out how his character should interact in a 3D environment.
Sega hasn't figured out how to fully utilize a fast moving character in a third dimension, without basically automating various obstacles or removing control from the player.
What you mean nothing? They've released various games in 3D with varying degrees of quality.
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Does anybody remember the days when SA2 had a better formula for control Sonic wise with stuff like timed jumps, Light Dash, Spin Dash, Homing Attack and Bounce?
Then on to Heroes they started over, adding interesting new stuff, yet messing up some things like Dropping Timed Jumps, Spin Dash, bad Light Dash functionality, and he couldn't even handle curves in the special stages? He felt stiff as hell, and the best playable character was Espio? I ain't even gonna get started on how poorly thought out Flying Mode was.
-Anybody remember how bad the Mach Speed stages were in 06? He was perpetually moving forward with no control, yet the levels were filled with detailed stuff and diagonal slopes despite the fact that he couldn't run them without getting hurt. Or the fact that Sonic couldn't handle a curve properly at all? Remember how it was so bad, that Sonic couldn't even remain consistent on platforms he ran on like those loops from Wave Ocean? How it was damn near impossible to steer him?
Remember in Unleashed, he finally had smooth control, and a new mechanic that allowed him to drift along tight areas? His Light Dash was functional, his wall jump was good, responsive and useful, as well as his other skills? They even designed so he can run on water if fast enough?
Remember in Lost World when um... He could run on walls and shit with the parkour and the tight block like movement?
Remember the sweet love Sonic made to the wall in Sonic R because you couldn't control him worth shit yet you still came in first place?
We've come a long way.
We had triangle titties, now they round.