I downloaded Sonic 4 today for the Xbox, and I just finished playing through the first two levels.
I haven't finished it, but I like it so far. The physics are different, but nothing worth complaining about. They just take some getting to.
And the homing attack that everyone was complaining about, I think it works out pretty well in this game. It's not like the badniks were ever that much of a challenge anyway. The homing attack just helps Sonic move a little faster.
The special stages are fun (I got four emeralds on my first try :D ).
The two bosses I've fought weren't too difficult, but they don't really need to be.
I like the music and sound effects. And the level of difficulty, i think is very good. My mother, who has never mastered a single video game since Pacman, was able to pick it up and finish the first level (with a little guidance from me). However, the levels get progressively harder, so they're not too easy.
Can't wait to see how Super Sonic handles. I hope I get to him before my brother does. (I'm watching him play now. He's got five emeralds.)
I do, however, think some of the objects might be a bit too big (such as the rings, and the big-headed flickeys), but that's minor.