It's a metaphor, you guys!

Rating: 8/10 (15 March 2018)

I'm writing this just because I see a lot (more close to ALL!) of reviews that are completely missing the point.
I too was annoyed by the plot holes and the inconsistencies of the script, like sending an inexperienced team in a suicide mission, radio won't work but nobody brings a cable with them, no tethers, etc.
Then I got to the end of the movie and realized the film is a gigantic metaphor for cancer. They LITERALLY enter a tumor, like if it was the Earth herself to have grown a cancer and we see all things that happen from cancer growth, how each person face it or fights it, and how it is ultimately alien, but still a part of yourself.
Watch the movie again with this in mind, and you'll be definitely more able to appreciate its finesse.