Lighter and Softer: in the original series, set in its own continuity, the Celestials experimented on primates and created the Humans, the Eternals and the Deviants. Yes, you read it right: the human race very existence was caused by Ancient Astronauts. The setting was then incorporated to the marvel universe, fixing the conflicting points when doing so, and the Celestial intervention was slightly changed: now they created just the Eternals and Deviants, the human race evolved on its own.
Mainstream Obscurity: Like much of Kirby's 70s Marvel work, it's hard to find in collected editions, and the ones issued some years ago are out of print.
Audience-Alienating Premise: Almost nobody was clamoring for a revival of the Eternals, and those who were probably weren't thrilled to see Chuck Austen reinvent the series as a story about a bunch of horny assholes turning the human race into their slaves.
Complete Monster: In this 2003 Marvel Max miniseries based on the classic Marvel characters, Kurassus is the deranged second-in-command of the Eternal army, and sticks out as vile even when competing with The Celestials. A sexual sadist who happily follows the Celestials' plans in wiping out entire planets of species, Kurassus takes numerous females of whatever species he is currently annihilating to rape and brutally torture to death, invoking revulsion from most of the other Eternals. Expressing nothing but disgust and hatred for every species that isn't himself, Kurassus begins brutally murdering any of the Eternals who try to make their lovers have equal intelligence as themselves, in one notable case killing one Eternal's lover in front of him just to torment him. After nearly being killed by the leader of the Eternals, Ikaeden, Kurassus unleashes dozens of abominable aliens to slaughter any Eternals loyal to Ikaeden, while Kurassus himself severely damages the frontal lobe of Ikaeden's lover, Jeska, reducing her to a superstitious wreck terrified of all Eternals. Even when beaten by Ikaeden, Kurassus continues to taunt him about his lover's condition, and dies while cursing him and the rest of his kind for all eternity. Serving as an Expy of Satan himself, Kurassus's sadistic and warmongering personality made him the worst of the Eternals by a considerable margin.
Critical Research Failure: The miniseries had a Show Within a Show about aspiring superheroes competing to become registered under the Superhuman Registration Act, which had recently become law in the Marvel universe. The show bears absolutely no resemblance to the way that Registration actually worked. Though, considering the amounts of Take That! towards Civil War, it wouldn't be surprising if Gaiman admitted to not bothering to see how the Registration functioned.
Epileptic Trees: The casting for the film called for an "unnamed Greek God", leading many to suspect that the film will also introduce either Hercules or Ares.
Unexpected Character: Even with Marvel Studios' track record of making formerly obscure characters like the Guardians of the Galaxy into mainstream hits, the announcement of an Eternals movie caught many by surprise. When the rumor was first leaked by gossip sites, some were even accused of lying due to the supposed improbability of Marvel actually making a movie out of the Eternals. It should be noted that in the comics Thanos is an Eternal, but this was retconned out of the MCU. Which probably made the Eternals as canon MCU characters seem even more improbable.