It feels to me a bit like cheating nowadays when i write movie reviews that end up needing to be marked for spoilers and basically end up describing the whole plot. In some cases, where the spoilers issue encompasses so much of the movie, it necessitates either an incredibly short, concise review amounting to little more than "stuff was happening, then WOW watch out stuff changed! I didn't like it" or a play-by-play of the movie in full spoiler mode. In some cases, spoilers for a movie or TV show can actually be what entices someone to watch it (in my case, i had absolutely no interest in Battlestar Galactica the 2004-2009 series until I read spoilers on how the series ended, and so I gave it a shot and absolutely loved it)
This is one of those films where its surprise twist encompasses basically the entire conceit of the film. Without it, the film has no reason to exist. As such, it's down to either a quick summary of my thoughts, or a full (or limited) play-by-play.
Luckily, my thoughts on it fit in the title. So for the spoiler-free review, you've already read it in the title.
As for the rest...
This film looks and comes across as a pretty standard fare science fiction alien invasion type thing. It takes something of a risk (in my opinion) by casting Michael Peña in the leading role, a guy who has been around for a while and in a lot of things, mostly as the token hispanic or the sidekick to the main hero. Nothing in his performance can be faulted; the problem is the way his character is written is just flat-out boring.
The main character guy is an ordinary John Everyman who loves his wife and kids and is a perpetual disappointment to them and constantly apologizing. The only interesting thing about him is he's constantly having nightmares about an alien invasion, nightmares which get so bad that he's passing out for hours at a time and missing playdates with his kids.
We're only briefly teased with these dreams being something more when he goes to a mental health place and sees another guy talking to him about his own identical dreams. Rather than delve into that or make a brief mystery out of it, they blow their load early and have the supposed alien invasion unfold that very night.
For the next 10-20 minutes is some utterly unremarkable action/survival scenes in which the John Everyman and his family and some friends over for a party must escape their apartment building as the aliens blow up chunks of the neighborhood. It's ably shot, though completely dry and rote, very much aware that it's been done before, and done better, both in terms of storytelling and in terms of action and exploding setpieces.
To skip ahead just a bit, pretty much all the major action scenes are like this; ably executed, but thoroughly unremarkable and ordinary; background noise and filler material to pass the time while you're left thinking about the big revelation of the movie.
And that brings me to the main conceit of the film, one for which they could have done a far different movie about that could've been far more interesting and fun:
The "alien invasion" is humans.
It turns out John Everyman's dreams were not some manner of prophecy of the future; they are memories of the past, because he is an android and his wife is an android, and decades ago they were all droiding it up while humans freaked out about the threat of AI, briefly and very, very lightly tapping on some of the same emotions, prejudices, and discussions about immigration --- there's literally a news panel on TV the protagonist is overhearing with a pundit clamoring hysterically about how the synths are "taking all our jobs".
Maybe the casting of Michael Peña in the lead role was meant to or could have played some manner of role in this, the hispanic Michael Peña as the ordinary "other", target of baseless racism and prejudice, only not because of his ethnicity but because he's a robot.
But nothing is done with this. We get a very brief expo-dump from one of the human soldiers captured alive, where he reveals to the protagonist that, after all the violence and fear against synths, humans went and tried to "decommission" them all with extreme violence, leading to a synth uprising which somehow managed to force all humans to flee to Mars, where the captured human soldier guy was born and raised, having spent his entire life there, prepping and waiting to take back Earth.
All the while the protagonist and his wife, having found his android children and adopted them, got their memories of the war wiped so they could go on living the exact same life for 50+ years, apparently oblivious to the fact that they never age or change in any way.
So much could have been done with this concept, either from the Humans vs Androids angle, the Humans as Aliens angle, the two whole generations of humans being born and raised on Mars, anything and everything, and instead they went for a straight-forward ordinary action movie as utterly indistinguishable as virtually any other in the "alien invasion and human resistance" genre.
It actually makes me feel bad for this film and the people involved; they aimed high with their ideas, then proceeded to do almost nothing with them in the execution. This is probably one of the absolute best "Could Have Been" films I will probably never see.