The new documentary Winnebago Man (2 screens) may seem like a lightweight entertainment, based on an accidental viral video phenomenon, but in a way it has more potential than many heavier documentaries. Any documentary about a single, living subject has the best advantage. First, you have the actual person to interview for the camera, rather than his friends and family, or "experts" on his life. Secondly, you have an entire film to devote to this one person, rather than dividing up the running time among many participants in a story. The greatest documentary ever made, Terry Zwigoff's Crumb, managed to plumb the depths of its subject's soul for an astonishingly "complete" portrait, all in just under two hours. Of course, Crumb interviewed some other family members, but they only served to underline and compliment the big picture.
It also helps when the filmmaker has a personality that compliments that of the subject. Another great example is Errol Morris' The Fog of War, which spent 95 minutes grilling former U.S. Secretary of Defense Robert S. McNamara about Vietnam; the purpose of this film was not to solve anything, but to establish that even a direct question-and-answer period with one knowledgeable person does not come close to solving the problem of war. Morris' used his unique interviewing and camera techniques to emphasize the slippery, elusive nature of the subject.