Take one: Director William Greaves presides over a beleaguered film crew in New York's Central Park, leaving them to try to figure out what kind of movie they're making. A couple enacts a breakup scenario over and over, a documentary crew films a crew filming the crew, locals wander casually into the frame: the project defies easy description. Yet this wildly innovative sixties counterculture landmark remains one of the most tightly focused and insightful...