Decent
The story is pretty solid (A lot more then most spirte movies) and the fighting is pretty good too, my main problem was with how repetative the backround is during fights. I know a lot of people are going to say "Alvin Earthworm this..." but for the most point they have a point. Alvin's fights are top notch, interesting and fun to watch. My advise would be watch SMBZ episode 6 (the last one on Yoshi island, I think it's epi 6) and just take notes on the fight scene in that. I felt kind of bored watching the fights in your flash at times.
Other than that, it was pretty good, the drawings I'm going to assume you did yourself for metal sonic was good too. All in all, 8/10 and 4/5.