Sorry I am writing this from work so no template to use.
First impression
This hits on a couple of different perspecitves - but if it is the boot in the stirrup I am meant to focus on I can not make it out clearly ... I am concerned that the black and white is overkill - but others don't seem to have mentioned this.
Subject
Meets the challenge - but as mentioned i think is a little on the dark side:)
Composition
Good this I really like ... cropping os the main of the beast is on thirds ... cool idea.
Brightness and technical stuff
I am not sure ... I like natural light .. always have .. but in this picture the boot itself is lost ...and I think the reason is the black adn white ... the contrasts in this don't make the boot pop - like it would against the natural colour of the horse.
Final note
I think this is cool. You did good and I know are going on to better and better pics.
Private message me if you wish any clarifications.
Love it - the off center subject with a cool horse and nice textured sand really makes for a nice shot.... I did not even notice the boot at first - just the stirrup - great lighing effects... wonderful composition