With Joshua Oppenheimer’s The Act of Killing you’d be minded to think that’s it, that’s the Indonesian genocide (1965–66) done, but now he’s returned with a second film that is equally stunning, equally riveting — in its horrifying way — and equally unforgettable. To have one such film in you, but two? I think it is now safe to conclude: there are good documentary makers and there are excellent documentary makers and then there is Joshua Oppenheimer, who is amazing.