If you watch the Spanish gameplay video, you'll see that it's not a total split. Modern Sonic still has his 2D sections, so it's not completely 3D the whole time.
Also, we have seen very little of the game, so I wouldn't jump the gun and assume they swept Colors under the rug. Stages could very well slow down a bit later on in the game, giving more of that Colors feel to the Modern Sonic stages. Of course they;re gonna go all out speed for the first Modern Sonic stage of the game, they want to "wow!" gamers with the "wtf speedz!". Anyway, I'd wait and see before jumping to conclusions.
As for Sharky vs. Sanus, here are my thoughts:
Taking ONLY the Sonic stages from Sonic Adventure under consideration, I'd say thematically and stylistically they are the greatest 3D stages every found in a Sonic game. They fuse real world with the bizarre Genesis era worlds and cover just about every environmental cliche found in the Genesis games. Gameplay wise, it was a nice fusing of the classic abilities (spin dash, spin attack) and modern powers (lightspeed dash, homing attack). However, my major beef with Sonic Adventure, in hindsight and compared to Colors, is that there could have been so much more (queue Bentley Jones song) to the stages. Instead of having Big and Amy stages, why not have 2 acts per Sonic stage? That's what I loved about Colors. Not only did I get to play a fun first act, but I'd also get five more acts in the same environment and each one I was playing as Sonic. Sure some were short or 2D puzzles, but they made much more use out of the environments than Sonic Adventure did.
Sonic Adventure 2 nearly perfected the Sonic stage gameplay: tighter controls, instant lightspeed dash rarely malfunctioned, much more fluid and varied stages. Despite the stages themselves not feeling as much like classic Sonic environments, they were very original and didn't feel like a lazy rip off of the previous game. City Escape and Emerald Coast are far more different than the Green Hill and Emerald Hill zones. However, my beef with SA2 was that I only was able to play as Sonic in six stages (plus 1 bonus stage and 1 final stage, though that required playing as every other character).
Anyway, point I'm getting at is that Colors really knew how to create a complete Sonic-only game. However, I totally agree that SA1 and 2 did a lot of things right. Personally, I'd love to see a game that combines the Sonic Adventure gameplay (slower paced 3D gameplay and the occasional speedy sections) with the stage structure of Colors.
Generations isn't quite that dream game of mine, but it looks to be close. I'm guessing we'll have 10 environments with 4-6 acts each, divided between Classic and Modern. Classic Sonic will give me that slower paced gameplay that I loved in the Genesis and Adventure games, while Modern Sonic will offer up the speedy gameplay. Hopefully playing more like a well paced Planet Wisp and Mazuri than this:
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I love the speed run videos for their craziness, but I also dislike how they get a bit TOO fucking fast.
