Due to the upcoming holiday, I couldn't resist.
"Horror" seems to be the only genre of game not based purely on a mechanic. "First Person Shooter", "Visual Novel", and even "Adventure Game" carry with it mechanical constraints, whereas "Survival Horror" distinguishes itself by the emotional reaction of the player.
Today, horror games have had some recent innovations in variety. While action oriented "Survival Horror" is the most visible, Amnesia: The Dark Descent and Five Nights at Freddy's have expanded the genre from the "Survival Horror" action-horror genre into newer avenues.
Five Nights at Freddies turned the "jump scare" into a mechanic, by forcing the user to specifically look for them (though these are in a specific order that the player must puzzle out). It's a game almost designed for streaming. I'm sure we will fnd more copycats in the coming years (especially since FNaF already spawned like 4 sequels in its short existence.
Amnesia: The Dark Descent uses a powerless player character and stealth mechanics. It's as much about environmental exploration as it is about learning how to run away effectively. It's a newer twist on hide & seek. This has already inspired copycats in games ranging from independent (Outlast) to AAA blockbuster (Alien: Isolation). Though I might personally credit this genre as going back to "Pac-Man" - limited agency, constantly about running and pattern recognition.
Finally "Survival Horror" has gone through many changes over its time - usually involving zombies. I'd credit Resident Evil as popularizing the genre, though many adventure games before than follows the same formula (Roberta Williams' own Mystery House spawned the Graphical Adventure Game genre). Resident Evil os a house filled with puzzles (see: 7th Guest), though now these puzzles can be interrupted by zombie attacks and boss monsters. It works by limited ammo, healing, and save ability. That said, the genre "evolved" into more action oriented gameplay, selling experiences of a badass protagonist against hordes of monsters (not unlike Doom). Resident Evil 4, FEAR, Dead Space, and even to an extent Alan Wake continued this pattern. Whereas survival horror used to be defined by limits on ammunition and healing, the aesthetics run counter to that. Notable exceptions are probably State of Decay and Alien: Isolation (also drawing from Amnesia) which use these elements in a far more limiting way than the Resident Evil franchise.
Finally, the recent adventure game resurgence - or the Telltale model of adventure game - brought on some new ideas in how to handle horror. Telltale's The Walking Dead creates a pseudo father-daughter relationship to heighten the stakes and make horror more about losing the love of another person - something brought forward to the AAA market for The Last of Us, which is sort of an action/stealth/survival horror mashup. The recent Until Dawn plays with interactivity in having the players' decisions affect who lives and dies and when they die.
What are some other ways to expand the feeling of horror in a game? How can it be more mechanically driven, or narrative driven, or mesh together for them? What design elements are underutilzed to create a feeling of horror?