Very flawed

Rating: 3/10 (31 May 2019)

I liked the first part, well acted and enticing. A mysterious intro, a classic portray of the family on holidays, and a strange night with a weird family standing in front of the house.
I liked that things picked up fast from there, showing the "doubles" surpsisingly fast and setting up the hostage situation. It obviously gets intriguing and paranormal with the doppleganger theme, but then it drops the ball. It becomes a slasher with useless one-on-one confrontations, and we learn that it's happening in many other places at once.
I have to go to the big reveal from here, and how it makes no sense.
1 - the doubles are shown mimicking mundane daily activities, dressed in the same clothes. This is silly. Where are the clothes from ? How do they replicate the "surface" landscape from their small square rooms ? Surely they don't have "crossing the street" practice areas.
2 - why the red suit when they practiced in copied clothes ? Either they want to replicate the surface version, or they want to differentiate with the red suit. We get both. (again where do the red suits come from ?)
3 - why did the swapped good version of the mother go insane and behave like that for the whole movie ? The predictable reveal made everything we saw prior to it make even less sense. She grew up underground in this hostile environment, and she had the same children but twisted ? She never used the elevator to get out ?
4 - the reveal has no weight. A good version underground gets bad, a bad version on surface gets good. The vilain is still the vilain, same for the victim.
5 - The red suits lines are just silly. It's just a useless mystery added to the mess. They won't stand against military or police, they're present all over mountains where there are no sewers ("you number 317, walk 2 days and stand on this hill to hold hands with 316 and 318 for no reason").
I like that the movie dared to give reasons rather early, instead of the usual "no idea, maybe-its-cliffhanger". But the execution and especially the background are seriously lacking. It all just makes no sense. At all. It just doesn't justify the watching time it takes to get disappointed.