Very cool to know! Thanks for the intel.
From watching the streams, it's looking to be the most pure "Sonic" of the 3D games.
Sonic Adventure 1&2 pioneered the 3D Sonic experience, at least when referencing the Sonic (and Shadow) action stages. Sonic Heroes dumped the non-Sonic stages and presented a full on 3D Sonic game. However, Heroes also mucked it up by making things too linear, adding multiple hits to enemies and making the "puzzle" of what character to use in each situation too easy (they had big color coded signs basically saying "Now be Knuckles!"). However the one big positive of Heroes was that it brought the classic 2D act, boss and special stage structure to a 3D game.
Colors looks to take the best of SA1&2&Heroes, adds in the 2D/3D switching of Unleashed's day stages, and tosses '06 and Shadow's contributions in the trash.
If anything, Colors seems to feel like the game that we should have received after Heroes (from a gameplay perspective). It has the 3D Sonic gameplay, optional powers (trading Flight and Power for Wisps) and the classic 2D structure: 6 stages, each containing multiple acts (around 5) and a stage boss. Sounds like an ideal mix to me!