My one qualm are the 3D platforms and environment. If Sonic 4 were too look more like this, it would then be more akin to the 2.5D segments of Unleashed and Colors which is not the direction that I'd want to see 4 take. I prefer the background and environments not to move with the camera but rather be fixed in place.
However the idea of the sunlight coming from the background to the foreground is a great concept and I'd love to see that sort of stuff in 4.