Hmm, I have a few problems with the first horse. =/
First of all, it's head. I find that, the neck is slightly too small and, compared to the rest of the horse, it's 'flat.' I think the... long bit of its face (*doesn't know how to describe it*) almost looks as if it is twisting away from the rest of the head. What could make it better, is if you shaded the picture. If you followed the shapes and 'bumps' of a horse, it will help you picture alot. Here's a picture to show you how a horse's face looks from that perspective:
I also has a slight problem with the front legs. They look 'static' compared to the hind legs. I think they would look either more tucked under or stretched out.
Sorry if I am being a bit vague. =/
However, your eye is brilliant!