You did a nice job with the shading in this pic there's definetely alot more here then in the rest of your pictures.

Alto you've made it a bit confusing where the light source here is. Some parts of the pic make me think it's coming from over head and others make it look like it's coming from the side. Also Derpy's hair... er mane should be casting some shadow on the top of her head.



Apart from that it looks pretty good