I'll just wing it and throw in some of the few games I would like to highlight for specific reasons. If this vote happens again next year, I'll hopefully have a larger pool to pull from.
1.
Alan Wake
Alone in the woods. At night. Try it sometime, it's ridiculously scary. And I don't mean "movie lighting darkness" ... pitch black. Alan Wake did that so well with its lighting in the woods sections. Plus the fantastic combat design that forces you to shine away the "Darkness" from the villagers before you can actually harm them with your weapons. Genius.
Plus that
incredible score (and
original songs of course!).
2.
ZombiU
I still haven't finished it but I feel it deserves to be on this list anyway. One lone zombie can be a legit threat if you don't pay attention or mess up while trying to take him out. Use your gun and risk attracting more. Swing your cricket bat and risk missing and getting hit. Manage your inventory on the GamePad while the game worlds keeps going and you might get attacked from your blind spot that you can only see on the TV. Shit is tense as hell.
3.
Resident Evil (2002)
The posterchild for how to remake a game. Watched a friend who owned the original game play through my copy of the remake and comment on all the things that were different and threw him off. It was magical. The gorgeous visuals sure did help too. And those fucking Crimson Heads. Holy shit, always have some lighter fuel with you!
4.
Resident Evil 2
While I came across Resident Evil (1996) first, it was watching a friend play RE2 and then walking home alone in the dark afterwards that first got me really excited about scary/horror games. There is just something about imagining yourself in a zombie filled small town at night, looking out for the sound of dragging feet and moans in dark corners. That was also the point in the series that really hooked me on the silly lore aspects.
5.
Dead Space
RE4 in space. Yea. Pretty much. Dead Space knew what made Resident Evil so great in the past. A very specific place you explore, tight corridors which both serve to make you feel boxed in and also reassure you that there's no dark corner you cannot see, the occasional big open space where that claustrophobic safety-net gets replaced with "OH SHIT A HORDE OF ENEMIES" and that Nemesis/Mr. X-like unkillable Necromorph that chases after you during certain parts. Holy shit. And that excellent lighting, UI design, sound design, character design, limb targeting. Damn.
Honorable Mentions:
DayZ (ARMA II mod version)
I've played this during the big DayZ craze. While it's overall more of a survival game where other humans are the biggest danger, my experience was more of a solo adventure and a god damn terrifying nightmare sim. Fresh game, I had no weapon, I was in need of food, and between me and (possibly) getting either of these things was a tiny beach town completely overrun with zombies. I spent probably an hour or so crawling on all fours through that zombie infested town, often mere inches away from certain death and trying not to make a noise while slowly removing myself from possible lines of sight that this is firmly cemented as an exemplary horror experience.
Cursed Mountain
A very flawed game but also a very unique one. Snow settings aren't that common in horror games for some reason. Usually it's houses, woods, spaceships or whatever. You're looking for your brother who disappeared on a hiking trip in the Himalaya. Unfriendly spirits don't like your trespassing. This is all about atmosphere. Snow is a great way to make a place feel foreign, claustrophobic (snow storms!), and dangerous. The constant ascend up the mountain serves as a nice visual progression that also raises the stakes and tension very well. If only the combat were better (you perform gestures with a spirit wand thingy to fend off the spirits).
Metro 2033
Look, Russia is scary. No, in all seriousness. Metro games are shooters, sometimes you just shoot other humans with guns. But other times, you find yourself in dark underground tunnels or a destroyed library (was it a library?) full with mutated monsters that react to sound (I think it was sound, been a few years?). Coupled with the general survival tension from the gas mask/radiation mechanic, this makes for a real edge of your seat experience.
Zero: Tsukihami no Kamen (Project Zero 4/Fatal Frame 4)
I have only played the opening bit of this so far but the way the series and this game specifically handles exploring spaces paired with the very tense "camera combat" against ghosts is a wonderful combination. You really do feel fragile and tense the whole time.
BioShock [on Survivor difficulty w/o Vita Chambers]
While it does get easier towards the end since you gain lots of abilities, BioShock on Survivor can be absolutely terrifying. Especially once you decide you need to take on a Big Daddy. My first one I spent running away and hiding in a vent from most of the time. The higher difficulty really goes well with the creepy atmosphere and disturbing nature of the Splicers themselves, while otherwise not really being a traditional horror game. While the game is extremely well known already, I still want to take this as an excuse to
post a great piece of score from it.