the anatomy for the full bodied horses deffinately need work.
the legs look stiff and boxy, if that makes sense. I'd sketch legs in motion and when they're stationary over and over agian. Try to make them look natural and not so stiff.
The pastern-to-hoof anatomy has no definition, it just looks like a box. Also, the eyeballs for the full-bodied horses are way too high and way too... humanlike. Again, sketch out eyeballs and horse heads.
In some parts, things just look boxy and unbalanced to the rest of the body.
This is something I sketched out a while back. See how every body part looks pretty much balanced with the rest of the body? See how the legs like natural and free flowing? See how you can easily pick out the pasterns, hooves, tendons etc.? That's just something to compare to/think about/work on.
Sorry if I rambled, I'm SO picky with the anatomy on drawings.
The anatomy for the horse heads are very good. The only thing I can say is try adding more detail, then they'd look more lifelike.
Can't give you a comparison for this one, because I usually just sketch horses and move on.
Can't critique the person, because I'm only good at horses haha. But from what I can tell, it looks really good!