You can take this any way you want. Scariest, most disturbing, most jarring, scariest because of -insert phobia-, etc.
Is it the game's ambience; the mood and atmosphere it creates; the hellish environment; its grotesque creatures; or maybe a combination of them all?
For me, I'd have to go with...
- Silent Hill 1/2 (ambience, atmosphere, creepy angles and views while playing, suspense, music)
- Treasures of the Deep (because of my fear of deep, dark, open water)
- Resident Evil 1, 2, and 4 (1 for the claustrophobia and pace, 2 for the hellish creatures, and 4 for the frights and suspense)
How about you guys/gals?