Definitely some solid work.
Some of the reviews here make me sad. I'd agree that this isn't everyone's cup of tea, so for those that don't like it for that reason, I cannot fault it. However, having grown up with cartoons like Ren & Stimpy and Beavis and Butthead, this worked quite well for me.
I admit that at first I thought the lack of quality illustration was due to a lack of capability, and even now I'm not QUITE sure that it isn't, but Sonic's serious look as Tails is crying, as well as the many amounts of different styles, makes me sort of doubt it. Either way, it very much works in the movie's favor, and matches its mixture of off-beat and cruel, gruesome humor. I pretty much had a good laugh at every single joke thrown in there, all the way to the 'Oh, nevermind' at the end.
In all, I had no complaints with this flash, and enjoyed it enough to watch it multiple times, which is why it gets a 10. I'm hoping you reverse the decision made at the end of the movie and decide to make more.