This dystopian thriller surprised me by the end. And not so much because of the doomsday reveal at the end, but mostly because of the approach taken with the story. It sort of reminded me of a Alfred Hitchcock episode, in which the characters try to figure out the mystery and make sense of their world falling apart around them. Literally.
Even more, the social relationships between two families and those around them in this situation makes for poignant commentary about this society and attitudes people have about it and people different from them. (In the sense of the "types" of people in it and how they interact.) Add in the fact that former president Barak Obama helped produce this film, one could get a sense of warning or even an "instruction manual" from it.
I have to agree with my girlfriend, as we analyzed this film over ramen, that aside from the creepiness of the deer in Leaving The World Behind, the most frightening aspect of this film is how people respond to their fears. (e.g. review bombing a film because of name association.) This and the mindset and materialism that would likely survive and be pushed into the future if this society were to collapse and somehow recover.