As an undergrad, I had a professor of Renaissance literature who contended that, if writers such as Shakespeare and Donne were resurrected today, they would most easily relate to horror films of all the possible film genres. According to my professor, writers of Shakespeare's period often dealt with the balance between good and evil, and would understand characters such as Jason and Freddy because they embody the perpetual, ever-returning nature of evil.
Horror films (especially slasher films) are rightfully criticized for being overly formulaic and not being particularly sorry about it. However, on occasion, a new horror film will add a unique and paradigm-altering component to the genre. Unfortunately, as a new horror films spawns sequel after sequel, it loses those qualities that gave it artistic merit.
I enjoy horror films because of the themes with which they deal. It's certainly not the character development.