It's a toss up between Project Zero, Silent Hill 3, Stalker and Bioshock had it's scary bits.
Project Zero was just constantly horrific. SH3 was one big mindf***k. Stalker was so unpredictable, you were just never safe. And Bioshock which owes much of it to it's atmosphere and the crazy people plus when I first came across a Big Daddy - I thought I'd be fine keeping my distance and plugging away with my machine gun, I'd not expected him to be THAT fast, before I knew it he was up in my business with his gigantic drill. It also had a few other set pieces which were pretty good.
Project Zero was just constantly horrific. SH3 was one big mindf***k. Stalker was so unpredictable, you were just never safe. And Bioshock which owes much of it to it's atmosphere and the crazy people plus when I first came across a Big Daddy - I thought I'd be fine keeping my distance and plugging away with my machine gun, I'd not expected him to be THAT fast, before I knew it he was up in my business with his gigantic drill. It also had a few other set pieces which were pretty good.