This film is erroneously assumed to be a typical Marvel Film, which is very wrong and I think one of the reasons why it has poor reviews. People expect it to be a typical hero movie with straight-cut morals and lots of focus on action and battle as the building blocks of friendship.
This is a very different fare from all that. Directed by Zhao, this film is more introspective into humanity through the lens of immortal creatures, and asks existential questions that are uncommon to that of normal Marvel fables. While it does try to answer all these questions in a very typical Disney-positivity style, the film's introduction of these themes about enduring ennui through cycles of horrible events, going against the greater good, and disrupting the norm are all themes I personally like.
The plot is a little special because it ties in these themes about the grinding wheel of time, what it means to be human and to have emotions. In a way, it is a less-heavy version of the humanist fable of Nier:Automata, which has the same themes about never-ending cycles of erasure, destruction, rebirth, and the will to continue. It's not the most original plot, but it gets the job done in delivering these themes.
The characters were all strangely well characterized as well, despite the sheer number of the main cast, within a single movie. I got to know these Eternals better than I did Black Widow's family in her movie, and that was far less people.
My main gripe is the decision to have the Eternals have human emotions, but that is a minor thing since every alien in MCU seems capable of human emotion.
The usage of historical flashbacks served the movie well, in my opinion, since I am a person who likes that sort of storytelling.
Overall, a very different Marvel movie and that is probably why I enjoyed it. I had seen mostly bad reviews or parodies of this movie, but I am glad I saw it for myself. The acting was great, and some of the tender moments were well paced and served to build a good foundation to explain why characters act the way they do.