Like many great directors, Steven Spielberg has something of an allergy to sequels. Among his 35 features, the moviemaker has made a lone direct sequel—1997’s “The Lost World: Jurassic Park”—and directed multiple films in just a single franchise, the Indiana Jones series, which, after “Raiders of the Lost Ark” (1981), begat three Spielberg-directed entries. An image from ‘Close Encounters of the Third Kind.’ In modern Hollywood, Mr. Spielberg’s reticence counts as remarkable restraint, but it disguises the fact that, for nearly 50 years, he has been tending to what is a series of films in all but name. Call it his extraterrestrial trio: Starting with “Close Encounters of the Third Kind” (1977) and continuing with “E.T. the Extra-Terrestrial” (1982) and “War of the Worlds” (2005), Mr. Spielberg has pursued his abiding interest in the potential consequences of civilization’s contact with life from other worlds. Together, the films form a rich, sometimes contradictory but clearly distinct body of work within Mr. Spielberg’s canon. The trio will become a quartet with the release of his latest alien …