Like Blues has stated, there's not too many pages that have gone by in this topic where I didn't mention my disgust with this game, especially in its "young adult" and "middle-age" page numbers. 
But the gist? It all boils down to physics. For some people, perhaps, Sonic, as a character, is enough to get them to support a game, regardless of quality. That just speaks more to the notion that they value the character, more than the game play itself. That was never the case for me. I fell in love with the original Sega Genesis/CD anthology of games, because they had great level design and physics that worked well with the character's main concepts, that being momentum-based speed, rolling and platforming.
In essence, Sonic 4 spits on everything that made the original games what they were (yet directly invokes them, by being "Sonic 4"), by why of implementing wack-ass physics. And no matter how much the developers try hide it behind homages, throw-backs and re-using various enemy types/boss fights, my heart is not moved when the game doesn't play anything like those classic titles.
Case in point: Why is that I'm SLOWING down when I'm rolling along, instead of picking up speed? That kind of [parasitic bomb] didn't happen in the original series.
And then of course, things like this can still happen:
So yeah, there-in lies my beef with "new Sonic".
Oh right, thats pretty much the only thing I didn't like (Along with the weak-ass mid-air homing attack from unleashed and the rebound from the homing attack. Also those famous dimps 1 Million foot drops.). Casino street was painful for me at that one point with the classic style bowl.
Besides, some people are already hacking the [parasitic bomb] out of it at Sonic Retro. So you may have your wish of "Classic physics".
Doesn't mean you'll play it though.
Also, anybody try collecting all the rings in the ending sequence?