To me he looks sort of bony. I'm not sure if that is a proper word to describe it, but that's just my opinion. I'm used to stockier horses so this is just more of a personal preference of mine to see more muscular horses. But if you are breeding him to a nice QH I'd say go for it! By your description he sounds like he has a great disposition, and it might be a bad judgement on my part because he's walking. With a shoulder and hip dropped it looks uneven.