The relationship between Reigen Arataka and Shigeo Kageyama is so multi layered that I can't help but conclude that this may be the most well written anime I have ever watched. It is so deceptively smart. At first glance you'd think you are watching something stupid ,but as you get to know mob and reigen,then you realize that you are just not paying enough attention.
This show also has the best re-wachability factor of any anime out there. Even better than Naturo's.
As to whether this is the greatest anime I ever watched, I am still thinking about it. But I am sure that it is definitely top 3.