Emulate the silent hill games and the resident evil games
Amnesia is easy to run
Undying
The Dark Eye
Eternal Darkness: Sanity's Requiem
Alone in the Dark
Clocktower games
System Shock series
Dark Fall: The Journal
Manhunt 1&2 (get the uncut version of 2)
Realms of the Haunting
Shadow of the Comet
Ripper
Scratches
Seven Games of the Soul
Rhiannon: Curse of the Four Branches
Zork Nemesis
The Lost Crown: A Ghost-Hunting Adventure
Divi-Dead
Sublustrum (Outcry)
Phobos 1953
Anchorhead
The Residents: Bad Day on the Midway
Thief 1/2/Dark Mod (certain fan made missions)
Nosferatu
Resident Evil 1,2 3 and Code Veronica
Sllent Hill 1,2 & 3
Haunting Ground
Siren, Forbidden Siren and Blood Curse
Fatal Frame 1, 2 & 3
Harvester
Sanitarium
Blackstone Chronicles
Seven Games of the Soul
Personal Nightmare
Black Mirror 1-3
DarkSeed
I Have no Mouth and I Must Scream
Dracula 3: Path of the Dragon
Last Half of Darkness
Tomb of Zohir
Beyond the Spirits Eye
Shadow of the servants
Return of the Phantom
Veil of Darkness
Dead Reefs
The Thing
Temüjin
Black Dahlia
Twisted Lands Series
Call of Cthulhu: Dark Corners of the Earth
Cosmology of Kyoto
Midnight Mysteries Series
Dark Dimensions: City of Fog
Dracula: Love Kills
Alpha Polaris
Waxworks
Necronomicon: The Dawning of Darkness
The White Chamber
Overclocked - A History of Violence. (More of a psychological thriller than horror)
Penumbra
Extermination
Gabriel Knight 2
The Void (aka Tension, aka Turgor)
Parasite Eve 1&2
Dino Crisis 1&2
Cryostasis
Phantasmagoria
Fear Effect
Cold Fear