Marvel’s Eternals could have been deliberately constructed as an answer to the company’s critics who complain they make the same movie over and over again. If nothing else, Eternals does try some new things. Long stretches owe more to 2001: A Space Odyssey and Prometheus than The Avengers. The film introduces an elaborate new mythology of ancient gods, aliens, and monsters to the existing Marvel Cinematic Universe. Some of that mythology features interesting ideas — most taken directly from the original Eternals comics by Jack Kirby — about the connections between superhero fiction and religious iconography. But every scene is burdened by an uneven cast and a leaden script crammed with millennia of backstory that repeatedly kills the story’s momentum.