To begin with, this film was awful. Just because Dirty harry directed it, that doesn't mean it's any good. It sucks badly.
J. Edgar Hoover did so much damage to the so-called "criminal justice system" it's a miracle it works at all, even as cruddy as it is. This man and others like him were instrumental in setting this country on it's path to self destruction. I truly believe that he knew that JFK and subsequently, RFK were going to be murdered. He was a deeply bent individual who did this country more harm than can be comprehended.
I don't think a person should judge a film based off how much they do or do not admire the real-life person the film is about. This movie really wasn't that bad. I found it quite fascinating and it definitely managed to hold my attention. Also, I know nothing about the real-life J. Edgar Hoover, but I quite liked Leonardo DiCaprio's portrayal of him, whether accurate or not. He brought a certain vulnerability to the role which made me very sympathetic to the character.
One thing I didn't like about this film, and I find this to be true with most of Clint Eastwood's movies, was the cinematography. It was so darkly lit almost the entire time that I could hardly ever see the actor's faces clearly. I prefer a film that is more brightly lit, I really don't like dark scenes at all to be honest, although there are certain cinematographers who I believe handle darkly lit interiors and/or nighttime scenes quite well. For example, I just rewatched Se7en on Blu-ray the other night and I found the cinematography to be lovely, despite the fact that most of the film was shot in lowly lit interiors.
Anyways, the film wasn't that bad. I think people should be fair. It actually really gets on my nerves when people allow their attitudes towards a person or issue to get in the way of accurately and realistically judging a movie.
Seven was shot Digitally, that makes those interior, darker scenes much easier to clean up, especially on Blu-ray. This was shot on film and then to help differentiate between the 20's and 60's, Eastwood wanted a Very Dark Picture. I personally loved the Cinematography per usual with an Eastwood film BUT I definitely understand what you're saying. Fincher is famous for his dark lit Cinematography as well but I'm pretty sure everything he's ever done has been Digital.