Despite the momentum behind the Marvel Cinematic Universe’s recent releases, The Eternals has garnered the lowest rating of any Marvel film, currently holding a 47% among critics on Rotten Tomatoes. In addition, it will likely be one of the lowest-grossing films, having only surpassed The Incredible Hulk and likely Captain America: The First Avenger.
There are a variety of reasons this could be happening. The film introduces unfamiliar characters and even casual comics fans may not have known The Eternals was a team in the Marvel canon. In addition, it received less overall hype than other shows and films released this year.
However, the property could have been doomed from the start as the source material is rife with confusion and other issues that make The Eternals a hard sell even for die-hard comics fans.
Jack Kirby’s Inspiration

The comic follows a world where all-powerful beings called The Celestials visited Earth 1 million years ago and experimented on the distant ancestors of humans creating the Deviants, humans, and the Eternals. The Deviants are grotesque beings with unstable genetics who live beneath the Earth and sea, while the Eternals are immortal beings who have been mistaken for the gods and heroes of mythology worldwide.
While readers today might not find this to be a new concept, it was incredibly novel for its time. The problem is that The Eternals author and artist, Jack Kirby, took inspiration from an infamous book that spawned modern UFO conspiracy: Chariot of the Gods? by Erich von Däniken.

Like The Eternals, von Däniken’s book questions if the myths and technological prowess of the ancient world were the results of ancient astronauts (i.e. aliens) who gave this technology to or directed these societies. However, ancient astronaut theories tend to focus on non-Western cultures, such as the Incans, Mayans, and ancient India and claim that these societies were too primitive to have possibly created the pyramids, the Easter Island heads, or any number of things.
So, at its core, The Eternals is already based on a highly bigoted, Eurocentric idea. Kirby has the story begin in an Incan temple with an Eternal named Ajak claiming to have been one of their ancient gods, following the example of von Däniken.
Though, it should be noted that Jack Kirby never claimed to believe these theories, but was more inspired by the limitless possibilities of such a premise for a story.
This alone would make many issues for any story, as it takes agency away from a majority of the locales and civilizations that could be used as a setting. Beyond this, there are also issues with the story itself.
Confusing, Incomplete, & Unrelatable Storytelling

The main conflict of The Eternals is that the Celestials have returned to Earth for the fourth time and have begun a judgment that will determine if life can continue. It’s a classic apocalyptic Marvel storyline that should have set the table for action and drama… but it didn’t.
In Jack Kirby’s run, it’s unclear if the Eternals are for, against, or even ambivalent to the Celestials. Ajak seems enthusiastic to return to his role as the messenger for these God-like beings, and Ikaris seems sympathetic to the humans, but the characters never do much to address the planet’s new visitors.
This is largely a result of the storytelling. Kirby starts arcs, but never finishes them, or has them move on to the next beat without addressing what came previously. For example, the Eternals chase down a robotic Hulk, but forget about him when faced with their ancient foe. In another arc, they form the Uni-Mind, a merging of all Eternals into one massive brain being, but return to normal in the next issue without explaining why it was necessary.
Another chip in the storytelling is the lack of urgency presented by the Celestials. The beings’ judgment lasts 50 years which is simply too much time to make any moment dramatic or stressful. The stakes aren’t in the face of the reader enough, and this isn’t helped by the incomplete storytelling either.
On top of this, the Eternals themselves are fairly unrelatable, being 1 million years old and unable to perish. Though the Earth would be destroyed, these immortal beings aren’t able to be destroyed without something that can completely scatter their atoms. Their age is too high to conceptualize and their invincibility makes it extremely difficult for readers to relate to them or feel any fear of impending doom. Unlike Superman who has a degree of attachment to the reader because he grew up as a human, the Eternals are too far removed.

Marvel seemed to have realized this when they later tried to continue Kirby’s run in Thor & The Eternals: The Celestial Saga. This series features the Eternals sparingly, and the main story involves a complicated adaptation of the opera Siegfried where Odin made a deal with the Celestials and had Thor live as a mortal.
Focusing on an already familiar character gave readers something to hold on to, but it also used the Eternals as a framing device and not a centerpiece as the title would suggest. When the Eternals come to join Odin in the final battle against the Celestials, they are quickly dispatched and do not contribute to the Celestial’s departure in the slightest. In many ways throwing Thor into the mix also made things even messier…
Merging With The Marvel Universe

Originally, Jack Kirby didn’t want The Eternals to be a part of Marvel’s comics universe. This is apparent from its construction as the likes of Eternals Zuras and Thena already had counterparts in Marvel’s Hercules series as Zeus and Athena. It also would make little sense for the humans to worship the Eternals as the gods of myth if they already exist in comics.
In addition, the antagonistic Deviants live in Atlantis in the beginning Eternals comics, but in Marvel, this is the realm of Namor the Submariner. With Atlanteans living much-extended lifespans, it would be hard to explain why they hadn’t met the Deviants after all of this time if they lived in the same/similar places.
What this meant is that the Eternals weren’t necessarily a happy marriage with Marvel canon, but there were some creative attempts to weave them in as best as possible.

In Thor & The Eternals, the writers’ main technique was to have the characters discuss how confusing it was to have people and places with similar names, but then move on. As this series focuses mostly on Thor and the Asgards, it doesn’t address much except in one respect.
This series seems to suggest that every pantheon exists because human belief sprung them into existence. Since the Eternals were allegedly the inspiration for these gods, it could be deduced that the legends inspired by these immortal beings caused the belief needed to fashion the Asgardian and Olympian realms.

However, during this series battle between the Olympians and the Eternals, it is revealed by the Eternal Hero that some of his exploits were a case of mistaken identity with Hercules. This directly contradicts the previous theory as it suggests the Eternals and gods created their myths simultaneously. So, it’s still confusing at this point why Marvel’s pantheons and Kirby’s Eternals could exist together.
Shortly after this story’s end, Marvel began the work of better mixing the Eternals in with the rest of the universe which would culminate in 1985’s The Eternals: The Dreaming Celestial Saga.
Beginning in the pages of What If?, they retconned the arrival of the Celestials so that they didn’t create humans, but left them with some mystery gene and allowed them to evolve on their own. More backstory for the original Eternals was added that made another Marvel team, the Titans, a banished branch of these beings. The Titan’s antics while exiled to space is what causes the Kree to visit Earth and create the Inhumans.
So, these authors and artists commendably gave the Marvel Universe a more concrete idea of how all these stories exist simultaneously. However, they still didn’t explain why the Eternals and the pantheons of gods exist at the same time. In the grand scheme of things, this question remained largely unanswered, leaving the Eternals still feeling like duplicates in a character-rich universe.
Conclusion

So, while some of the criticism of The Eternals may have been unfounded, it also wasn’t given a steady foundation on which to build. Jack Kirby’s wild imagination may have needed some reins to polish a large idea, and give the story more focus. The publisher could have also tried to work with him to insert the characters more naturally into the story (though any comics historian can tell you Kirby frequently got the short end of the stick in this regard).
Overall, it seems an odd choice to use these stories as an integral chapter for this phase of the Marvel Cinematic Universe. The producers could have something very specific in mind for The Eternals that will improve what was given, but that is a lofty goal. With what’s at hand, the MCU has a lot to overcome to make The Eternals as hailed as their other films.