I absolutely adore your human facial structure. The straight sides, and the rounded chins plus the beautifully puffed up cheeks are always impressive, and cute.
I love Dinky's annoyed expression. I love the circular scribble style of her pupils, and the beautiful shine and color of her golden eyes. The eyebrows and that absolutely adorable mouth pretty much complete the expression. Her body is also excellently posed. I absolutely adore how you managed to make a very good looking head looking back, along with her very angular legs. They were very great looking anatomy-wise, and were absolutely adorable and perfect for such a young character. Her tiny, sausage finger tips on the muffin were beautiful. The really short, sleeveless dress was lovely, in the way it kinda reminded me of a Little Sister from Bioshock. Her ear was lovely, in its cute elongated C style.
The sweat drops on Derpy were excellently done. I love the subtle, barely perceptible mixing of the grays that make us miss just how much tiny detail went into making the sweatdrops look as natural as possible. The stress lines around Derpy's eyes were lovely. I love the way the muscle movement is so clear and distinctive to nervousness. Her eye was beautiful, particularly with the doodle like quality of her pupil; it mixes so well with the egg yolk yellow eye. Her eyebrow was nicely done in its helix like-style. The crumbs on her face and the smile while chewing a muffin were lovely. I love how her cheeks puff out from the muffin she's eating. Her ear is lovely. Great work with the grey shirt.
I love the wooden wall, plush carpeting style of Derpy's house. I'm not a stickler for either, but it just seems to work, along with that 50's boobtube showing My Little Pony (excellent touch with that). The semi-transparency and the random scribble style of the pictures on the wall were excellent; I don't know what it is about the lack of clean lines on the wall that I like so much, but I think it may be the fact that they still form definite shapes.