The area the nose is placed and the lack of a shadow on the nose together look... weird.

Great idea i like it!!
BUT Sonic's mouth is weird......

Thanks for you comments. One day i may have time to add some of the mentioned ideas and found mistakes.

also, he has two left hands D:

good work on the dithering, though.

the foreshortening on his right (left side of the image) hand doesn't work, so it just comes off as extremely stubby fingers, or the face of a crooked gardening hoe.  The other hand and the hedgehog have nice smooth lines that follow the action, but the eyes are a little too straight and rigid, more circular would work better I think.  His mouth could also be a little higher and needs depth. 

the idea is great, although there is something that doesn't allow to be really satisfied with the picture... more like sonic's desing is kinda off