This was..........astounding. The film does take a bit to get going, but it's better for it. If you're looking for a direct adaptation of the book(s) this isn't it. I just finished the first book a couple weeks back, and I can see where Garland pulled some individual elements and used jumping off points for his story, I almost don't want to read the second and third installments because of what others have said about the story, and I would hate them to sully how I felt leaving the theater after this film.
The film echoes the first book in that it takes it's time in the beginning. Allowing you to be enveloped by the shimmer and Area X. There's a haunting beauty to it, there's plenty of time for the viewer to make their own assumptions as to what's happening in Area X before they spell it out for you. Even then that only gets you to the end of the second act. The third act is something completely entrancing, and hypnotizing. I did not want to breathe. I hate the word trippy, yet it fits, it has some of the most engrossing and engaging visuals I have ever witnessed on film. Imagine a 20 minute Tool music video.
I'm so happy. Some may feel a bit of a disconnect toward Lena the biologist and some of her motivations, but I was sold. Horrifying, and beautiful. Best way to describe the pacing would be Alien/The Thing, and instead of frenzy at the end of those films, you get a revelation that grabs you by the throat.