He's got an short neck, underneck, and a pretty steep shoulder. I agree that he's camped under, and looks a little long through the back but that could be an optical illusion. Looks like he toes out in the back also, but I can't quite tell without the proper conformation shots.
All of the listed are common within the 'old style' quarter horses though, so I'm not sure if they should still be considered faults or just to standard.
I've got a lovely bunch of Neuticals,
There they are all standing in a row
Big ones, small ones, some as big as your head