So let's see if I got this straight:
Knuckles - Is guarding the Master Emerald when Robotnik, Metal Sonic, and Nack attack. Nack runs off with what appears to be the Master Emerald, Angel Island falls, and Knuckles gives chase. In reality, Nack's emerald is a fake. Robotnik and Metal Sonic have taken the Master Emerald to build a fortress/superweapon around Angel Island. Knuckles catches up to Nack and fights him. Sonic and Tails show up and destroy the fake Master Emerald. By now, Angel Island is converted into Robotnik's fortress.
Sonic - Him, Tails, and Amy are chilling on the beach, when a tidal wave created by Angel Island falling ruins their vacation. They go to investigate, whereupon they discover Nack hassling Knuckles and save him by destroying the fake Master Emerald. Robotnik makes his move, Nack kidnaps Amy, and Sonic goes off to stop him. May or may not end in a fight with a roboticized Robotnik.
Tails - Follows Sonic until they are split near the end. Fights Metal Sonic.
This might be a bad idea, but maybe each character has his own boss? Sonic would fight Robotnik in a machine as per usual, Knuckles fights Nack with a new weapon of some sort, and Tails fights Metal Sonic with either a new body or some stage-related gimmick, maybe?
In reference to the new Amy design: I like it, but the legs and boots should really be shorter, as has been said. I would lose a row of buckles and have them end at her knees. The hair would look at lot less weird if the sides didn't curve outward at the end. Have it curve inward instead, maybe make her spines a little less round, and it should look a bit better.
This post has been edited by Veemon: 06 February 2009 - 03:40 PM