I'm impressed, no really, you've done an excellent job. Not only do you use shading, but it fits in with the old school style that was reminiscent in Sonic Adventure and Sonic Adventure 2. I see throwbacks to Sonic R and even Shadow is remaining true to character at least in the modern sense. Character movements are smooth despite using stiff object movement to represent animation. I dig the fact the characters almost walk like they had a wireframe. I don't know if the shading for anything but the main characters is appealing, nor do I think the texturing is all that great for background scenery.
Compared to most Sonic Flash, this one is original through and through. No sprites have been used, music has been done tastefully, and some effort has been given to overall choreography. No, I take that back, the choreography looks like something out of Sonic Adventure. This was a blast to the nostalgic past and I have you to thank for it. Great job and keep it up.