It seems to me that of many conventionally understood narrative genres, horror is a genre that has some particular peculiarities in regard to the relationship between its audience and whatever form of media that horror takes, be it film, novels, or video games. What I want to describe, I could probably also connect to other genres as well, but I think that horror (and, perhaps, comedy as well) requires more of its audience in regard to the attitude with which that audience approaches its material to begin with. There is a kind of contract, perhaps, that horror seems to almost require its audience to sign off on, a responsibility towards the form, that often is not so explicitly asked of the audiences of other narrative genres.
What I mean by this is that horror is somewhat more easily “ruined” in some way if the audience chooses to take the wrong attitude towards the material of horror itself. The audience of a film or reader of a novel or player of a video game can potentially and quite deliberately wreck the mood and atmosphere that horror intends if they want to. If, for example, one approaches a work of horror with the idea that horror is in itself necessarily campy, it is pretty easy to break the mood intended by a slasher film. You can laugh off the situations the characters find themselves in (and allow themselves to get into), the gore, the grotesqueness, etc., etc. by simply taking the proper pose in relation to these elements of that subgenre. Frankly, simply throwing open the windows to let sunshine explode into the room while one plays a survival horror game can rend the atmosphere of a horror game apart rather readily.