I read the trilogy, here's my spoiler free take!

Rating: 8/10 (28 February 2018)

Having read the trilogy, I knew going into the movie adaptation that there would inherently be shortcomings. But I was intrigued to see a world I could only imagine before:
Positives:
+ Visually stimulating, dare I say gorgeous. A satisfying experience to see what before I could only read about.
+ Essence of the trilogy's plot and main sci-fi ideas are represented
+ Erie/creepy feeling was also recreated on the big screen
+ Casting was decent
+ 18A gore and violence...
Negatives:

Too many cuts and alterations to the plot/story, leading to other problems...
Poor character development, especially outside the protagonist
Dialog is too direct and doesn't match the mystery of the story
Pacing issues, considering the early reveals of where the plot was going
Missed opportunities to add to the story with dialog/narration

Summary: As a standalone movie, it breaks some of the mold to a traditional Hollywood flick. It's weird, creepy, unexplained, unique.. the same words I'd use for the books. Visually stunning and story captivating, I recommend it.
If you REALLY liked it, I strongly encourage you to read the books, even just the first one. Everything is more elaborate and intensified within the book, and with such significant plot differences, it will feel like your discovering the Southern Reach for the first time! Enjoy :)