Here is my critique,
-Make the snout less thick, slightly shorter and straighter on the top.
-The forelock would never be that long to cover the eyes on any horse.
-The neck is at an awkward position, it wouldn't be like that unless the horse is reaching for something.
-The nostril is not that wide unless the horse is agitated and is flaring it.
-The ears should be rounder, less erect and set in stone.
-Don't be afraid to get in there and put in all sorts of details to emphasize the muscles and bone structure.
Hope it helps. =)