A few things that I noticed are that in some of the pics your horse is actually behind the bit. Also, a few pics it appears that he is heavy in your hand which is pulling your upper body forward, this is affecting his ability to move off of his haunches because your weight gets put onto his forehand. Otherwise really cute horse awesome stretch in the hind end. One more thing. I believe you are leg yielding in a couple picks. In leg yield there should be no bend in the horses neck or basically he should be straight througout his body, and you are leaning!
I love the pics though, he is gorgeous I wish my horse had that much extension in his hind end!