Documentary is not a genre, but an entire branch of movie-making. So pitting diverse qualifying contenders against each other to determine the 33 best... well, that's difficult. And when you're coming down from the wildest election in American history, it's even more difficult.
Have I included enough music docs (Don't Look Back, Gimme Shelter), foreign entries (Tokyo Olympiad, The Sorrow and the Pity), or issue-driven films (Super Size Me, An Inconvenient Truth)? I'm definitely missing great shorts and series (Night and Fog, Civil War, The Staircase, the Up films), as we've limited the list to features longer than an hour. And movies that mainstreamed the form, like Nanook of the North, The King of Kong, Crumb, The Endless Summer, Capturing the Friedmans, Paris Is Burning, Spellbound, Bowling for Columbine, The Times of Harvey Milk, and The Fog of War, did not make the cut.