I don't have much of a problem with the homing attack, so long as it is not used as an excuse for lazy level design, whereby you zoom over miles of bottomless pits, jumping from enemy to enemy. I think it can be implemented cleverly and can be a logical advancement from classic Sonic gameplay.
Also, I actually liked Sonic 1 and 2's aesthetic more than Sonic 3's...the original games just had a bit more style. I would have liked to see a "combination" of sorts with classic pixel art, but I don't too much mind the style they've come up with. The new Sonic is still a major problem for me, because I think the character design is godawful and not in the least bit fitting for what's supposed to be a classic Sonic title. People always bring up how Mario's design has changed when talking about this, but really, Mario has changed with every iteration--from the NES to the SNES, and from the SNES to the N64. Also, these changes were incremental enough, like color swaps, etc., that most people honestly didn't notice. Sonic's new model looks radically different from his old one.
But it will all come down to the gameplay, and I am deeply concerned by some of what I've seen. There are still levels that play themselves, as Aki mentioned, and classic Sonic level design has been replaced by Rush-inspired material. Sega has delayed the game and claimed they listened to the complaints of fans, so this is actually encouraging. But my expectations for Sonic 4 are high, and I feel I'm justified in that. Sega must deliver or risk the death of their mascot.
And reviewers and gamers MUST remember that while speed has been Sonic's selling point, the best Sonic games were about good level design and platforming. That's exactly why so many fans (myself included) believe Sonic 3 and Knuckles to be the best the series has to offer.