Well, the worst aspects of fan films are usually bad cinematography, editing, vfx, acting, and writing. Rogue One has all of those. What makes it like a fan film is the subject matter, to which I would say who cares.
It has some of the best CGI (not including Tarkin and Leia) EVER.
Even that is commendable. I don’t think I’ve ever seen better rendered CGI humans before. It’s just not perfect, which is what it needed to be to not draw criticism.