Describing The Act of Killing as a film unlike any made in the medium’s short lifetime almost feels like the definition of hubris, or at least hyperbole. But Joshua Oppenheimer’s wholly unique exploration of the genocidal horrors lurking in Indonesia’s recent history earns every bit of the praise accorded it since making festival rounds this Spring (notably IFFBoston) and beginning its limited theatrical run in July; if critics describe it as a masterpiece, that’s because it is a masterpiece, an exceptional display of daring that will secure Oppenheimer’s name in the annals of cinema. That The Act of Killing also happens to be one of 2013’s most unsettling and insightful releases should…