Without giving too much away, I felt that the plot was extremely harmonious in describing and showing something very dark and cynical. Very well-crafted. I have never seen themes and devices that were so broken and pessimistic woven together so carefully and resolutely. An incredible experience.
Unlike Bong's Snowpiercer (in Bong's words, the "corridor movie"), which seemed a lot more overtly dismal and outwardly bleak, the darkness is latent and truly hidden below in Parasite (in his words, the "stairs movie"). The initial, more superficial reason behind the name of the movie is almost instantly revealed in the first twenty minutes, but you never truly understand the significance of this name until towards the end of the movie. And the way the plot was carefully constructed, layer by layer, and then how these elements are all resolved is extremely original and disturbingly gruesome. Then when you think that's bad, finally, the movie resolves with something again dismal, and more viscerally dismal.
There are also some marvelous plot motifs which you might not even notice until you think over and over again about the various themes that pop up throughout the film. They all complement the story extremely well, and each of their ultimate purposes are not revealed until later, or until one looks at the unfolding as a whole. Extremely engaging film. I would like to watch it again and again.