Some good ideas here, but the execution fumbled.

Rating: 6/10 (28 February 2018)

First, I haven't read the book it was semi-based on. All I knew about the movie was from the trailer.
I described the movie as "It's like The Thing, if The Thing was sort of lame."
So these 5 women go into this slowly spreading extraterrestrial-infected area called the Shimmer, which looks like a bubble on the outside, with the faint swirling colors. Why 5 women? Someone notes that it's been almost exclusively men before, so let's try it. It's kind of a suicide mission anyway, they wanted to go, so why not? The movie didn't make a big deal out of it, and it didn't turn out to really make a difference in what happened.
The interesting stuff: Lena and the psychologist have a conversation about how humans seem to self-destruct and sabotage themselves in one way or another, that it's inevitable. Lena talks about how God makes mistakes on a genetic level. Lena is a biologist who researches tumors. There are some tattoos that are really symbolic, though Lena's seems to show up halfway through the movie. (I thought it was on the paramedic at first, and that Lena assimilated her, but I was mistaken.)
All these ideas end up juxtaposed with the Shimmer, where everything is in a constant state of growth and mutation. It's all around them in nature, then it infects them too. They react in different ways to this realization: one snaps, one gives up, one finds the source and assimilates into it, and Lena tries to fight it. But how can you fight it? You can't. You can only become it.
There are some great scenes. The best is when a certain creature attacks them... absolutely horrifying and unforgettable. Also outstanding is when the women find a man who had something growing inside him, and it must have burst out of him because they find his skeleton stuck to a wall, his ribs and skull some 15 ft higher than his legs, all in a mass of colorful mold. They find a field with trees growing in the shape of people. Were they people at one point? We don't know, and it's fantastic.
The cons:
It takes a long time for the movie to get to the part with the Shimmer.
I didn't feel attached to any of the characters, and they all had interesting backstories hinted at via a few lines of dialogue.
There was one incident in Lena's past that the movie flashed back to 2 or 3 times, and it was really distracting, and unnecessary to show it more than once.
I thought the mirror person scene was too long, the SFX of it dodgy, and its "destruction" was ridiculous and obviously not going to work.
There was not a drop of humor in the whole movie. One of the women nervously trying to joke around would've made sense.
They could've done a little more with the "what is an identity, what makes me *me*?" idea.
The scene where the psychologist was in the center of the lighthouse was too short: that was really interesting and we didn't get to see much of it.
What does it mean that cells are refracted?
When they first get in the Shimmer, they realized they don't remember making camp, and it was probably 4 days since they entered. I thought this was a setup for them starting over every day, not remembering anything that happened before, so they'd have to write notes to themselves, etc. but it never gets brought up again. That would've been really interesting.
I felt like it was worth watching at least once, but I paid too much to see it. When my dad rents it or it comes to Netflix, I'll probably watch it again, if only for those scary scenes.
In the theater, one guy next to me fell asleep, and maybe the one on the other side of me too. I wasn't sure.