Not bad. Custom chars are always a good way to be original as long as you introduce them slowly and don't go overboard with creating too many. The story is unremarkable and my interest is nuetral. If you make another, I will watch it. If you don't make any more, I won't really care.
I noticed that some of the sprites, such as Eggman running and Knuckle standing, were moving really fast. Try adding a few extra frames to slow them down and make it look more natural.