My favorite Black Mirror episode of the first two seasons, in part because it takes the complaint I consistently have with the show: the concept and its morality swallowing its human characters whole (and not in a metaphorically fitting way), and reverts that. The technology and the commentary on it are a natural, subtle extension of the story of how grief can stop us from moving forward. Not coincidentally, it also has the most fully fleshed out character, whose agency of choices in her own story make her more than pawns to the plot like most characters in other episodes (only "The National Anthem"'s scale benefits from that kind of inevitability, in my opinion). Of course, it helps that Hayley Atwell is phenomenal in the role, giving each choice of her character's heartbreaking arc full emotional weight. Also nice that even while having the humanism countering the show's nihilism more than usual, the episode still doesn't avoid some disturbing touches here and there, including its ending, which manages to be both beautiful but very chilling.