“[Noah] Baumbach has a wary gaze and speaks in careful loops of retraction and calibration; it’s hard to imagine that he spent years doing improvised comedy, during and after college. … [Greta] Gerwig, who is twenty-nine, also has a precise, literate mind, but she is more buoyant, and sometimes has the air, not uncommon among her contemporaries, of having swallowed a very low dose of LSD.”