The characters are bad and we never really get to know hem enough to care about them, the young girls had no purpose in the movie outside of doing dumb stuff despite being over 50 years old. Penã's character was alright since he actually had some decent character development throughout the movie, him coming to terms with them not necessarily being the good guys felt earned.
I loved the twist in the movie, that the aliens were in fact not aliens, but rather humans who had been driven from earth by their own creations, it's a good twist and the 15 minutes revealing the twist is by far the strongest part of the movie.
It felt a little weird that the synths that retained their memories wouldn't have kept track of the humans and warned everyone else shortly before the invasion began, it also seemed weird that the synths hadn't taken measurements to protect their home against the humans at all costs.
The ending was a little weird because of how confusing it was, obviously the synths will go to war with the humans, but was this the only synth city in the world or what is the deal with them looking out into the nature while they ride under ground to the secret base thing?
And holy shit at the train track CG at the end, I am not even sure what they were going for and it confused me so much. Was the train tracks supposed to be destroyed or did they submerge into the ocean? They also lower them so fast that it never could seem believable. Also when the elevating platform crashes down early on in the movie, I couldn't stop laughing at how it seemed to fall with 3x gravity enabled and how the bad editing made me believe the neighbors wife was still on the platform when it fell. The kids also had a flashlight while on the platform, but they don't get that flashlight until the mother gives it to them in the scene right after the platform falls down.
I think the biggest success of the movie is that I want to learn more about the world the movie takes place in, the twist is so strong that I would honestly watch a sequel just to know how it all plays out once all the cards are on the table, but otherwise it's pretty forgettable.