I <3 him :) I was never a fan of fresians until I worked at a dressage farm that had a morgan/fresian cross in training. When he was collected and using himself I felt like I was going into battle... lol :) I never knew much about them before then so I never took to them, but after riding Teddy I've become a fan. It was especially cool to have that big mane flowing around me... except when it blocked my vision... :)
Anyway... as far a critique, I actually dont think his back is too long, he is somewhat smaller in the hind end than the front, but I think that's pretty typical? And from your avatar it looks as long he can use his hind end just fine. :)
Otherwise I have nothing negetive to say, he has a really nice expression :)
"The white horse moved like a dancer, which is not surprising: a horse is a beautiful animal, but it is perhaps most remarkable because it moves as if it always hears music."