Phnom Penh Lullaby is a John Cassavetes-style documentary—about a bickering couple, no less—but one will not find amusingly rambling scenes of middle-class drunkards quaintly skirting their troubles. Here, the handheld, jerky camera lingers on sad babies, sad prostitutes, trash-strewn streets and some of the saddest domestic squabbles ever recorded on film. Depending on your personal taste, you will either be riveted or exhausted—even bored