I think it's multiple things:
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The intentional cheesiness of it all of course
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"...in you" :soviet-bashful:
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That lil earnest, close-lipped smile Vault Boy has as opposed to his usual wide, toothy grin
The best Fallout 4 poster is Mr. Pebbles: The First Cat in Space.
In my headcannon Nora is the power armored soldier shooting a Canadian POW in the head in the Fallout I intro cinematic.
https://www.youtube.com/watch?v=geLiEiAiQJA
That poster kind of reminds me of Gremlins 2, which was a masterpiece in many ways. One of its most memorable moments involved a contingency tape that was prepared for use in the (unlikely?) event of the end of the world. It shows some sentimental nature imagery, and a narrator says something like "because of the collapse of human civilization, Clamp TV is now going off the air. We hope you have enjoyed our programming, but more importantly, we hope you have enjoyed... life."
Those plastics aren't going anywhere, even after you die. :amerikkka-clap: