Is the movie simple or does it have lots of plot twists and intricate relationships between characters? If the latter is true, the movie's complexity makes it hard to understand.
When you see the word complexity, think of something with a lot of pieces, something not easy to put into words or understand. Things that can have complexity include: the events leading up to the American Civil War, a broth made with many ingredients, your relationship with your parents. Complexity is the opposite of simplicity. When something has a lot of complexity, you say it is complex. When it has very little complexity, it is simple.