I didn’t find the “plot holes” mentioned problematic at all. The team is scientists, not military, so tactics surely aren’t their forte. This is established both when Portman outshines the others with weapons and when they don’t instinctively form a battle plan - they’re not tacticians, they’re scientists.
As for the found footage scene, I thought they didn’t jump on the EMT’s ramblings for three great reasons: 1. Portman’s character is in shock 2. The crew is afraid of each other going crazy and are walking on eggshells with each other so as to avoid one actually going crazy and tying them all up. It happens anyway, so this fear is well-founded. 3. They want to see what the pool looks like currently. A lot is going on.
As for the poor strategy of recon missions, it’s established that the first couple of days inside are complete memory wipes, so it’s unclear whether any missions would have success trying to turn back once inside. After all, not one single human makes it out until Portman’s character firebombs the place.
As for the film, I found it to be primarily interesting as a fantastical dip into a dark universe. The human elements seemed incongruous to me, and I just didn’t put much effort into intellectualizing after multiple on-the-nose flashbacks. Seemed like a dead-end. The pure fantasy was interesting, even as it has a quasi-Heliocentric finale. I do like that there’s no implication that the foreign entity finds humans all that special, as if it came specifically to Earth for the magical humans. It seems far more random - it does its thing where it lands, and all sorts of strange possibilities seem available. As far as thrillers go, it far outshines some more “terrestrial” fare that ends with a clean victory for the good guys. There’s no telling what is won or lost at the end, except the magical Shimmer full of nightmares. What’s the last thriller you saw where the “enemy” is a “magical force”, and when the film ends it’s not defeated and yet it’s not necessarily a bad thing? Novel, if nothing else. I expected no Koreeda and got none, but that’s hardly a strike against an oddball alien film. The alien is far more interesting than the humans, or other humanoid films of its ilk. Something to appreciate, even if if’s not an all-time great, or a humanistic landmark, or even philosophically intriguing. Perhaps the villain in the film is not the alien but despair, and self-destruction merely a side effect. The alien, then, is not the villain but the setting: “How a group deals with despair inside an alien world.” Cleverly, the film kills off the most self-aware character first, leaving the less prepared ones alone and defenseless - against themselves. The alien isn’t the villain, after all.