I have not looked at the screens, but compared to the art of the classic games, it seems somewhat hard to make many fully 3D sections on Chemical Plant Zone as a good amount of the level is on tubes (hopefully ones you can spin into). I am not really too sure as to what to expect as I am hearing about explosions and stuff too, but I did not want the exact same style of level anyways.
On the people complaining about the 3D variations of levels... Remember all those times where you fell off Speed Highway and got frustrated at lame hit detection? Imagine how much more fun it will be with lame hit detection, unresponsive buttons and BOOST! I am sure the Sonic & Knuckles level is also going to be tons of fun ! :'(
Probably my biggest problem with the modern styled Sonic levels is how they all use similar gimmicks, which was a major issue for Unleashed. Like, why do so many levels have balloons floating around? Just to bounce on? Why not just make a different gimmick for a level like City Escape that has no need for random balloons?
But even though I like the "Unleashed" style of gameplay a bit, I do not think it feels very Sonic-like. I like that they are reintroducing rolling into the games, but it is really strange how against it Sonic Team are to begin with.