Well, C.C. (my initials, too, btw)
There's some interesting things going on here. The ears are really attractive. Horse ears have very complex Concave/convex curves and lines. I think you have a good feel for that. The throatlatch area and neck is good, too.
The muzzle is, hm m m. Almost there. I think the nostrils are a bit overworked. They, like the ear, have complex curves, but it's ok to make them a bit simpler for clarity, unless you want theat to be the place people spend the most time looking.
The eye on this horse is what's off. You have it looking more like the eye of a human , or dog or cat; an animal whose eyes are in the front plain of its' head, and this view is a bit from the side.
A horse's eyes are more positioned on the side of his head, so when viewed from the side, you are actually viewing it full on.
Look more carefully at the skull of a horse and how the eyes fit in, and where the ears are (further back than in your drawing).
I hope you don't mind my nitpicking, but if you are doing a focussed study, some attention to anatomy will be essential.