On my cell, so didn't look at the video... Stifle is a tad too high for my liking. But the angle of the picture isn't great, so can't comment on his hindquarters, which could easily compensate. Leg might be a little on the straight side, but again, picture is no good for second half of the body. Shoulder isn't my favourite either.
The angle of the photo is why he looks like he has a long neck.
I'm not the best for picking apart conformation...but I just wanted to say he has a very cute face! But, as Crimson said, a cute head isn't a reason to buy a horse. He does look like he may have weak-ish hindquarters, but I think the picture angles are a bit strange.