The one genre we can safely write off as completely wank.
The sole appeal of these films is in their suspense. And that suspense is never creative or imaginative. It is only ever around the notion of: "this character may now be killed by the murderer".
Also, the majority of people that love this genre of film are girls. Make of that what you will.
FAO: anyone considering defending it by using 'Psycho' as an example - please punch yourself in the face first.