Having just written about a good horror film (The Human Centipede [First Sequence]), I think it only proper to explain what I think makes a bad horror film. For that, I need look no further than the film I just saw last night, The Haunting of Molly Hartley.
I won't say this film is all bad. It had nice schoolgirl uniforms. Nor would I call it an incoherent, laughably inept mess of a film, such as Plan 9 from Outer Space. That would be rating it more highly than it merits. Laughably inept horror films at least provide laughs. The Haunting of Molly Hartley prompted little emotion at all, other than a strong desire to check my watch.
The Haunting of Molly Hartley, you see, was dull, and that is the worst thing a horror movie can be. The purpose of a horror movie is to present you with the illusion that a new form of being--a deformed destructive being (DDB)--has entered the world and is threatening to destroy you. That should not be dull. If it is dull, the horror movie is failing at its job.
Molly Hartley is dull for a number of reasons. The settings are bland, the dialogue is without crackle or spice, the acting is wooden, the plot is a copy of other copies of Rosemary's Baby, and at no point does anything surprising happen. Even when some hallucination or other pops out from behind Molly, accompanied by a loud noise, this is expected by the alert horror movie fan, because that is the sort of thing that happens at about this point in this kind of movie.
The worst disgrace of Molly Hartley is the lack of a strong DDB. Molly is supposed to turn into a demon or devil-servant or something on her 18th birthday, and we can expect that this makes her the DDB. But she is not physically deformed (aside from a scar daintily obscured by her decolletage), and although she is supposed to be spiritually deformed, she exhibits this deformity largely by adopting a mean schoolgirl manner common to the other mean schoolgirls around her. Perhaps this is supposed to be a comment on the banality of schoolgirl meanness, but it succeeds only in being banal.
Nor is Molly very destructive. She breaks a girl's arm and kills a couple of people, but her heart doesn't seem to be in it. Possibly actress Haley Bennett's heart wasn't really in it.
The greatest virtue of The Haunting of Molly Hartley is to clarify what makes a bad horror movie. This, in turn, makes the good ones scream louder.
Deformed and Destructive Beings: The Purpose of Horror Films