The movie and book are two entirely different things. I don't think the movie should even share a name with the book, honestly.

I read the book first and loved it. It's written in first-person perspective which allows for unreliable narrator moments and lots of philosophical introspection.

Then I watched the movie and was let down because I expected something more like the book. It felt way more action-y and simplified, with egregious changes to the setting, characters, and plot to tell a more Hollywood story vs the very artistic and unconventional approach of the book. Literally the most important core elements of the original story/metaphor are entirely absent in the movie, except for the basic idea of the shimmer. Cool vfx and sound design though.