Serian looks like a horse with a lot of personality (really sweet face and very alert expression), and after all, isn't the very most important factor?
As for conformation, he is long backed and does have an upright shoulder. The first thing means that his back will be weaker but it can also mean a more comfortable ride for the human, and that horse will be better able to flex laterally. Conversely, it will be harder for him to flex longitudinally (get his croup tucked under and his rear legs well under himself for collection) The more you do to strengthen his back and develop lateral flexion, the better he will be. Upright shoulder means a bit more jolting ride. Oh well . . .
I don't see a real problem with the pasterns. Maybe a little difference in angle. Maybe the farrier is trimming him too steep (taking off too much toe). I think you must know better than us how he FEELS when yo ride him. His conformation isn't text book perfect. Are you a perfect rider?