It is a stunning work of art! The only critique I have is to maybe soften/lighten the inside of the eye a bit because it seems out of place on such a light, detailed work. The eye is the focal point, but because it is mostly black (I do see some colour at the corner), it really dosn't have as much soul as it could if it had more rich deep browns and such in it. I find that oftentimes a horses' eye will look much brighter in real life than it appears in a photograph, keeping this in mind will help to make a drawing look much more realistic and give it more character.
