Jeez, now you’ve really gotten me started. Great documentary films that are heavy, but kind of on the long side: Shoah weighing in at 9 hours, but I remember when I was watching it, it felt kind of like a book, something that I could pick up and put down and pick up again. And Spike Lee’s When The Levees Broke about hurricane Katrina and New Orleans is another great one. That’s only 4 hours long.
And Burden of Dreams about the filming of Werner Herzog’s Fitzcarraldo is another great one. It might actually be a better film than Fitzcarraldo was.
And again, another lighter one. Errol Morris’ Gates of Heaven about a pet cemetery and pet cemetery people, both the ones that run it and the ones that bury their pets there. It’s not necessarily as good as Thin Blue Line, of course, but it’s more fun.
And so many people have already mentioned The Fog of War…