Very nice sketch, although it seems to have shadings on it that look like an area that would be colored white (or maybe it's just my imagination) but if they are supposed to be white, then it's not a friesian but some other sort of feathered horse. Cause Friesians are always pitch black unless they have some sort of cross breeding. I raise and train friesians. E-mail me and I'll send our site.
Other than that, it's very nice! Keep up the good work!
Formation of the animal is good. Legs in nice proportion to body. Head and neck horses eyes are set more to the side of the head. Neck needs to be slightly longer.