He's cute(: This guy has a bigger, less attractive head and big unattractive ears. He lacks muscling all over, but his working on his topline will dramatically improve his appearance. His croup is too sloped for an Arabian, as the breed standard is to be as flat as possible.
Overall, he's a nice guy. Lounging with side reins and a surcingle will really help his muscling. If you're not sure how that works, I've seen some pictures around the forum that I can dig up for you(:
Good nutrition will work wonders for him. Possibly feeding him free choice grass hay, small feedings of alfalfa, and a complete senior feed would be a good choice, as well as a senior horse supplement. Also, make sure you get his teeth floated and that he is on a rotational deworming schedule. The fact that he's a rescue leads me to believe that he probably hasn't been taken care of in those regards.
His poor feet look terrible – I hate how people just let that happen because they're too lazy to take care of it and instead neglect it and cause big problems for the poor horses. It makes me angry!! >
But congrants on your rescue boy – he has loads of potential! :)