In an interview about 12 Years a Slave, director Steve McQueen was asked what mattered most when making a great movie. He replied, "Story, story, story." Writer and Director Bong Joon Ho could teach a master class on that subject.
Parasite has twists and turns, but it's never smarter than the audience. You see each one coming, or suspect something is coming, or know you could have seen it coming. Every event, every character, every prop, almost every line of dialogue has an echo later in the film. The craftsmanship is amazing.
A family of four---mom, dad, adult son, and adult daughter---live in a tiny apartment in a slum. They all work at whatever they can to get by. The son seizes an opportunity to get hired as a tutor in the home of a wealthy family. He fudges his university degree to get the work, but he's fully up to the job. As scams go, it's pretty benign.
This sets the two families on a collision course. I won't reveal anything beyond the opening minutes of the movie, because you should enjoy each delicious revelation for yourself.
Let's just say the movie is completely satisfying for its suspense, its social satire, and its profound questions. Usually we're satisfied if a movie does one of those things well. How rare it is to get all three in one movie.