The thing about horror, the main thing, is to create fear in the viewer, and you do that by instilling a sense of vulnerability. You can do this in several ways:
- First, by introducing uncertainty. This is something that games and movies neglect horribly nowadays. Most of the time you see the scary parts coming right away... The music builds up, everything seems to stop, a lot of focus is given to a specific "trigger-action", and it always happens... Often with barely any build up... A good horror movie or game will trick you often, so you have no idea when the music and setup are a queue for something horrible, or just building your suspense over nothing. You never see it coming. This is, by far, the best method of instilling fear and horror. One of our most basic instincts, we fear what we don't know, what we can't predict.
- Making you feel weak (mostly regarding games)and the enemy strong. By introducing enemies that can't be killed (even if they're easily avoidable), or that seem almost unphased by your attacks, even if they die. Being outnumbered also helps. Why are one of the all time "horror" classics, The Zombies, so scary if done right? They're an horde of undead, you can only kill them by a blow to the head, they don't feel pain, and don't back down over threats, or even if you rip off their arms or blow their legs off, this kind of "resolve", "determination" is very frightening...Even if it's not really resolve or determination but pure mindlessness. Another good trick in gaming is to make the enemies possible to avoid, but far easier to kill, then granting only scarce ammunition.
- Shock value. Often delivered in the monster and scenario designed. Anyone remembers the hospital level from Silent Hill 2 (I think)? Anyone remembers how much it messed you up to see the faceless, misshaped, mutilated and rotten nurses, holding the dead freak babies, in the blood and rust soaked halls of the hospital? I think there's few scenes in gaming or movie history that are more shocking, because it messes with basic principles of our culture: Hospital, place of healing, safe place; Nurses are healers, people we trust, often with our lives; Babies are helpless, innocent... Silent Hill took these concepts and turned them inside out. For some reason there's few locations that can be scarier than a hospital if put under the right (or wrong) light.. which leads me to another point...
- De-contextualization. Removing things out of context. The human mind is one of habits, of familiarity. It is naturally comfortable with things that make sense, that are under the normal context. When something suddenly escapes the norm it is aberrant, it is weird, it's disturbing, peculiar. Take, for instances, American Mcgee's Alice [http://en.wikipedia.org/wiki/American_McGee%27s_Alice]. While a lot of criticism can be leveled with this game, there's one thing certain: the game is disturbing. Why? Because it takes one of the most cemented childhood stories of all time (Alice in Wonderland) and twists it, perverts it into horror.
- The gore. Ironically this is least effective method, and the one used more often by games and movies nowadays, often used exclusively, which makes it rather moot and bland. Gore should be used scarcely, cause the more it's used the less "shock value" it carries, specially in our society nowadays where we're constantly bombarded with gory movies and games. If used correctly, it can make a frightening movie/game nightmarish, if used wrong it just makes a bad movie a total joke.
If a movie or game has the user going "ok..ok..calm down...what's going to happen?...whaT?....What was that??What the fuck do I do now??Ahhhh!!" when there's nothing there, it won, it did it's job.
Sadly, nowadays, most horror movies and games fall too deep into "action", a good horror movie/game won't have too much action, as it empowers the viewers/players and detracts from the horror feeling.