If the neighbor has not cleaned up on his own, he may resent have a new person complain, whether to him or to the authorities. Some of these slobs make good neighbors - in other ways of course. Chances are you will piss him off by trying to get his place cleaned up. So, you block it from view , decide you can live with it, or buy elsewhere.
You could speak with your neighbor, discuss the situation, and offer to help him clean up his yard. In addition, I would plant a screen of fast growing trees like Green Giant Arborvitae across the back to hide the view and landscape with beautiful flowering shrubs in front. That way, you've added value and a focal point to your property.