This episode is a perfect example of great writing. The concept is fairly simple, and so is the message. However, what really makes this episode great is its relatability. It's one of the things which can make movies and shows powerful. The writer creates believable characters which are completely authentic. They then create a setting that the audience can relate to -- making the atmosphere feel as real, and familiar, as possible. Once a writer has done that, they're truly able to capture the audience, and draw us into the story.
My favorite genre is, easily, science fiction. This approach works, even for that genre. When a writer creates a relatable, realistic atmosphere with authentic characters, and then couples that with a thought-provoking, interesting concept and story (science fiction), the result is a timeless, powerful classic.
I give this episode nine stars because the writer "gets it". Not all writers do, so, well done. I can't give it a ten, because, in order for it to be perfect, for me, it'd have to entail a more sci-fi concept.
The show "Black Mirror", is probably the best I've seen, with this sort of thing; since it's predominantly sci-fi. However, the biggest problem with "Black Mirror" is that it sometimes has sexual content; which is always a minus, in my book.