That was impressive!
The animation was obviously well done, and in some places outright awesome. Though I do also have some complaints.
First, the art. Often the characters seems to have really big heads or tiny bodies. If the proportions were better this would have been perfect looking.
Second. the story. I have little clue what's going on, but I guess it's every good guy vs every villain all at once.
Third, sound. The music was good, though the songs did not always flow very well into the next song. Also, there were no sound effects for anything at all which would have improved it a lot.
Fourth, Quality. By that I mean, I wasn't able to change the quality by right clicking. I wanted to put it on low as some scenes caused lag and probably meant I missed some good animation.
Other than those few bits, this was just awesome! But, I guess I do have 1 last minor complaint. You gave Sonic a new transformation? He already has more transformations than just about every character ever made. Giving him more just seems pointless. Or was it meant to be one of his old forms? It looked new to me.