(I should start with the disclaimer that I'm not an expert on horror in either films or video games; most of what I'll be talking about is based observations from a few games and a few assumptions about what people find scary. If I say something that seems incorrect, correct me!)
One of the things that has a significant impact specifically on horror games is the fact that games are about control. Games as stories are often differentiated from other modes of storytelling by the fact that you have some form of agency, but this gets interesting in horror games because, often, horror is specifically about not having agency. Most horror movies I can think of include, as a major element, the helplessness of the protagonist. Alien leave the protagonists in space with few weapons and an enemy they can barely track that's as dangerous to kill as to leave alive. Trapping the protagonists, disarming them, subjecting them to an enemy that is stronger than they are and too incomprehensible to fight - this is how horror movies like to play. (Unless they're just throwing gore at you, but I find those movies less frightening and more viscerally repulsive).
Historically, video games have taken a different tack. Think about Doom:
|I think the walls frighten me the most, maybe because they're the most like something you'd see in Alien.|
And that might be at the bottom of why it's hard to make games scary: the "You Win" part. Part of the tension in horror movies is that often you don't know who will make it to the end, and often nobody does. At no point do you have any kind of security in the protagonist's safety. In games, on the other hand, you know that you'll survive until the end, or at least that if you die you'll be able to pick up near where you left off and continue. Games have toyed with taking this security away, but it's difficult to do without making the play seem meaningless. The ensuing catch-22 - make it possible for the player to have a happy ending, or take away the player's satisfaction at having succeeded - kills the horror at best and kills the game at worst. Even games I love, like Amnesia, had a tough time working out how to end the game in a way that felt satisfying and consistent with the narrative without reducing the suspense throughout the game.
So, how do games work with what they've got to give you a compelling horror experience?
The best way to turn the potential disadvantage of control into something that works for horror games is to limit that control in a frightening way. I've never been an especially big fan of the Resident Evil series (the walking-around controls were horrifying enough for me), but in the one I played - I think it was Zero - I was really impressed by how limited the items were. It was in a lot of ways not unlike Doom - there are enemies, you shoot them, they die - but the fact that you had an extremely limited amount of ammunition, health, gasoline (for incinerating downed zombies), and so on really brought the "survival" aspect of survival horror to the forefront for me. The horror games I've reviewed previously all got a lot of mileage out of limiting control as well. Amnesia took away your ability to fight back, and to look at monsters. Limbo made your character so frail that barest survival - sometimes requiring terrifying measures - became a triumph. And Home played so many brilliant tricks on the narrative that by the end it was really hard to say what you had in the way of control.
Home was June 2012. A game as recent as 2012 did something really cool and freaky and innovative with the genre, to the extent that it belongs in the genre at all. By comparison, I just watched Cabin in the Woods a week ago, and while it did some clever things in relation to the horror genre, it didn't feel like it did much that was interesting in the horror genre. A lot of what I've read about the film talks about praises it as inverting/critiquing the horror formula that has gotten so predictable, and while I don't think that's unfair I think it says more about horror movies in general than it says about Cabin in the Woods. Horror is far from being a dead genre in film, and people are still finding new ways to explore it. But the innovations in film itself have been relatively few in recent years, and that's what makes it so exciting to see games like Slender or Home do so well. I would say in general that there's a little more flexibility in what a game can be than in what a movie can be, and certainly there's been a lot less ground covered in games than in film - but that's making a more general statement about video games and other media than I'd like to focus on in this post.
At the core of it, I think the best thing video games have to offer to the body of entertainment that we call "horror" is the way the game mechanics - especially control or lack thereof - can be used to generate tension. This isn't just about adjusting difficulty, it's about specifying the means you have for interacting with the game world. The level of interactivity in Amnesia is almost perfect; you can pick up and throw objects, click and drag to swing open doors, and so on. The fact that these motions are all pretty imprecise - sometimes it's hard to open doors, sometimes turning a crank is tricky - actually helps the tone. The seconds spent fumbling at a door are often the difference between life and death, and when you're being chased by a monster can remind you of the terrifying nightmares where you everything goes wrong at the instant you imagine it going wrong. Home's matter-of-fact past-tense leaves you feeling helpless even as you make all the decisions that determine the story, because the story has already happened. And Slender's refusal to let you pause or tab out of the game force the pace so that you don't have a chance to recover from the panic it induces.
I wanted to use this post to tie off the string of horror games I reviewed, and I think at the bottom of it is this: Horror is about a number of emotions, but fear - arguably the core emotion - is evoked mainly through feelings of helplessness. When you put your audience in a position of control, as when they are playing a game, it's your job to balance that control, to find a way to keep that control from being arbitrary while at the same time giving them the sense of oppression and powerlessness that is so critical to evoking fear.