Superhero movies cannot be all things to all people. While Marvel Studios likes to pride itself on how its films can jump between genres so that something like Captain America: The Winter Soldier can be a “paranoid political thriller” and Guardians of the Galaxy can be a sci-fi romp through the cosmos, they’re still operating under the dictates of the superhero genre. That means there are clear heroes and villains, superpowers to dominate an external threat, and a need to save at least a planet if not a galaxy or the entire universe. A Marvel movie, by its very nature, can only go so far before it’s reined in by these dictates, which makes Chloé Zhao’s Eternals an exceptionally frustrating movie. In each character, you can feel a far more interesting narrative straining to get out, but at the end of the day, the genre mandates the use of superpowers to defeat a threat to humanity. What should be the core of this movie—what it would mean to witness thousands of years of civilization and your contributions to it—instead becomes window-dressing to a typical superhero narrative where superpowered beings have to defeat some world-ending threat.
Source: Eternals Review: Slamming Against the Limits of Superhero Cinema