Well he DOES go into pipes...
Modern Sonic is about Speed. Sonic '06 experimented with autorunning speed segments, and Unleashed solidified the concept into decent speed based gameplay.
Colors took what Unleashed did and polished it off, as well as including more 2D segments. And since they werent restricted to regions of the world anymore, they were able to do much more creative things with the stages. They also brought back Eggman as the final boss, returning some of his lost dignity along the way, and they shed the 4kids actors, leaving only Mike Pollock cuz hes just such a great Eggman.
And Generations is following suit by actually having Classic pure 2D sonic in the game, and stages based on old stages from all across Sonic's lifetime.
Wow Sega. Wow.
Its just amazing how they have come this far.
Maybe Mega Man will follow suit some day?
that said, Sky sanctuary [tornado fang] yeah. Although it looks nothing like what I would have imagined a 3D SS looking like. Its colors are totally off.