*spoilers*
This film was beautifully made. I loved how it runs parallel to our world and our history but reinventing it to fit the Enternals. All characters were fleshed out enough, to care for them. But honestly, what takes the cake is the story telling, the lore, the cinematography, the vision, and the many questions you were left with after the credits. Who, out of the Eternals, would I be after experiencing so much humanity? The bad and the good. How would I react after learning that my purpose/mission is against my own morals? how would I react if I were used for someone else's gain without my knowledge? Or to know that my memories were constantly erased for millions of years. The characters were complicated and valid in their own right. Needless to say, if you're trying to watch a thin-plot superhero movie with a clear villain and a hero with non-stop CGI fighting and nostalgic cameos, this is not the film for you. This movie goes beyond that.
In short, the Celestials reproduce by seeding a planet (similar to an egg and a sperm). They created the Deviants to clear out Earth of anything that would prohibit the human race of advancing and warming up the planet for the Celestial to develop and hash out of Earth. That being said, the Deviants evolved and became apex predators also feeding off the humans. This was a problem for the Celestial because this meant that humans weren't going to reproduce and warm up the planet. Because of this, the Celestial created the perfect being that wouldn't evolve and that would kill the Deviants: the Eternals (The Eternals weren't aware of the truth and thought they were there to protect humanity from the Deviants which, in their perspective, they saw as monsters). After the Eternals cleared out all of the Deviants, they stayed hidden monitoring Earth without interfering with the human race for them to develop through wars, advancing their technology/medicine and exponentially populating Earth. However, when the Earth warmed up enough, it was revealed that some Deviants were frozen in ice and now attacking humans again. This forced the Eternals to reunite after thousands of years without interacting with each other. And of course, they had developed in different ways, believed different things, and had lost touch with the mission and each other. Not only do they learn the truth, but also learn that the Celestials create universes with many planets with life in them, to keep their species thriving. After the Eternals learn the truth, some battled with a decision: should we let the Celestial hash from this Earth and kill billions for them to create more universes and thus eventually creating more life? or should we kill the Celestial and save everyone on this planet?
The film leaves you pondering on the idea that everyone has their own perspective in a story. Are the Celestials bad because they want to continue thriving as a species while destroying planets but creating many more? Are the Deviants evil for evolving and wanting to continue their species? Are the Eternals evil for killing off a species they thought were parasitic to Earth? Is Ikaris evil for being loyal to the Celestial that gave him life?