Ok...I finally sat down, and played Sonic 4 though, I was a little drunk.
I enjoyed the graphics. The music and sounds had a nice retro feel to it, but I can understand why that might turn some people off. Some sounds just get downright annoying.
As some of you mentioned, the physics and some of the animations are just awkward and poorly put together. And it is especially noticeable since I recently played the older Sonic titles. IMO, its not a HUGE turnoff, its just something that will cost you a few deaths from accidentally landing on spikes/enemies until you get used to it.
The targeting system is very annoying to me. I loved it in the 3D titles, but it does not mesh well with the wonky physics.
I'll give it a 7/10
I can see this as a successful reboot for Sonic, but I hope the Sonic team uses the fans feedback when developing future projects and the developers actually have MORE TIME to fine-tune the little things that made the older games great.