First and foremost, this is a movie that critiques government ineffectualness and corruption and placing corporate interests over basic humanity. Watching this movie while knowing the context of the Sewol Ferry disaster and the blatant corruption, impeachment, and imprisonment of former President Park Geun-hye, you'd understand why it resonates with South Koreans. This movie blurs the lines between truth and fiction because while there are factual errors, the way that the fictional government handled the nuclear situation is how many South Koreans believe it would handle an actual disaster: lots of hand-wringing, cover-ups, and abandonment of its citizens to cover their own ass.
Amazing movie and be prepared to cry.