What would you like to do with him?
He has a long back and his pasterns seem a bit upright to me (I'm not really sure, you'll have to get a more knowledgable person to look at that), although his hocks look nicely angled and his front legs look nice and straight (a bit hard to tell with all that winter hair). His pasterns are nice and short and so are his canons. I really like his neck, it looks long, its balanced with his body, seems correctly built, and I think it ties on nicely. He has an upright shoulder (which is a bit small for me compared to his hip but that's just me being nit-picky) and high withers, a steep, short croup, and a nice big hip. He has a nice deep girth and his face is adorable.
Overall, although he's downhill and has some flaws, I think he looks like a solid horse and from what you've said he has an A+ personality. He has a nice amount of bone and although his shoulder/ pasterns are on the straight side, they are both the same angle. Horses with high withers and downhill builds seem to get sway backs easily, so I would suggest doing some exercises to build his top line if you get him, even if it's just for a pleasure mount.
Also, I'm no expert, so take what I say with a grain of salt. I'm pretty timid about being the first to critique a horse on here because of that, so hopefully those with more experience will get here soon and correct me if I'm wrong about anything.