Time Out says
Writer-director Cary Joji Fukunaga uses Mr. Scary Face as the catalyst for an unusually sprawling chase to the American border, impressive for a debut feature. Suffice it to say that three characters come to dominate the narrative: Casper (Flores), who hopes to escape a terrible trap; Smiley (Ferrer), his pint-size former friend and armed pursuer; and the waiflike Sayra (Gaitan), whom Casper attracts as a ward after a truly heroic act of defense. Sin Nombre means “nameless,” but for all its conventions, the film is hardly generic; the rainy, purple-hued vistas, many of them shot from the roof of a northbound train, are photographed by up-and-coming ace Adriano Goldman, and the nihilistic anxieties are raw and real.