This is a good shot with an interesting subject, good focus and good sense of action. Tthe reason it's not a GREAT shot is it's cropped on both the top and bottom........ when you have a tall subject like this and you want to bring it closer to the viewer, you must chose one or the other. You can only get away with cropping both ends when the subject is symetrical. Generally on horse shots you crop the hoofs unless it's flying over a fence or post and part of the picture. Another draw back to this picture is the horse seems more in control than the rider, who appears about to break into tears.
THe quality of the subject shot is quite fine, good exposure, the cropping of the top of the riders head and the front legs of the the horse really mars this.