If these Sonic the Hedgehog 4 videos are legitimate, the game looks good and about what I'd expect from a 2D Sonic on a current generation console. Since it will be an XBox Live Arcade game, I'm sure I'll be willing to shell out $10-$15 for it.
But I would suggest this to Sega -- zoom the camera out at times. Perhaps you could have it zoom out in proportion to how fast Sonic is moving. Capcom used a variable zoom level in Bionic Commando:Rearmed to great affect. I actually think anyone releasing an updated version of an old school game should look closely at all the things done right in Bionic Commando:Rearmed. The way it handles 2 players would also be a good model for Sonic. The camera zooms out as the players get further away from each other. When they get too far about, the screen splits. I don't know if Sega plans to make Sonic 4 two players, but if they do they should use the Bionic Commando system or one like it.