[youtube:2nsey78t]JZV5UNS2y60[/youtube:2nsey78t]
Hardcore physics
That video perfectly contrasts the old-school game's hardcore physics to the casual physics of Sonic 4.
Slower acceleration, uncurling, homing attack, and drop-stop physics are all casual elements to make the game more accessible to iphone casuals playing with their virtual d-pad and Sonic Rush DS playing kids.
Take drop-stop physics for example. It allows fast forward momentum while coming up with a cheap method to avoid over-shoot and diminishes the need for precision timing. Uncurling gives Sonic a little mid-air play requiring less accuracy from the casual player.
If you look at a lot of the review and fan feedback for Sonic 1 & 2 iphone there were a lot of complaints about the game being hard to play and too fast for the virtual d-pad.