Elizabeth thinks she detests Darcy because his qualities (or as she would call them, faults) are the opposite of what she prefers. He is not amiable, social, or talkative and so she assumes him to be arrogant, condescending, and mean. Also, they are from different social circles and classes. However, there’s an obvious attraction from the start and whether subconsciously or not, they are drawn to each other.
Nowadays, we have the good girl and bad boy binary, the wealthy with the lower class, the interracial relationships, the young with the old, and so on. The movies Knocked Up, Pretty Woman, and The Notebook are a few good examples. The question is what’s so appealing in what appears to be an incompatibility between two people?