Resident Evil first then a few years later Silent Hill. Those two kept me awake many nights in my teen years.

Silent Hill was the first video game I really played all the way through on my own (and was also on the first console we ever owned). I had played Mario, Sonic, Donkey Kong, Goldeneye, etc. at my friends’ houses, but that was the game that really started it all! I was already into horror stuff at that point, so it was right up my alley, though. I still think of Pyramid Head on foggy days.

Related, but PT was a fun experience when it first came out. Played it once on my own and then once with a group of friends!

One I haven't seen mentioned here yet was Metroid Fusion on GBA. My brother and I would play it at night, then have trouble falling asleep, convinced that every sound of the house settling at night was the SA-X coming to get us

We never beat it then, and only years later did I rediscover it and beat it. They definitely nail the feeling of helplessness, but it's so rewarding as the tides turn towards the end of the game

The 7th Guest was the fist one I really cared about. I grew up watching horror movies from the age of 5, but never really played a horror game until I got The 7th Guest in a CD-ROM drive bundle for Christmas of '93. It's not so much a horror survival game as it is a horror puzzle game, but a great game nonetheless. I'll never forget the opening: "Old man Stauf built a house and filled it with his toys. Six Guests were invited one night, their screams the only noise..."

My brother and I used to play a game called Splatterhouse on Turbografx-16. It was humorously horrifying, given the highly pixellated gore on screen.

Silent Hill 2 was creepy as hell. We'd all budle up around a TV and start it after the parents went to bed and turn off all the lights.

F.E.A.R. as well.

I also couldn't finish the Bioshock demo because I was too sacred so I made my brother play it for me.

Thief 3's Cradle level was formative in the way that I have never ever seen a better horror game. Overall I didn't like the game as much as the previous two. But the Cradle is unsurpassed.

The demo for Alone in the Dark 1 also lives rent free in my head because it was one of the few games we had back then. Plus the graphics were absolutely astonishing. But I never knew how to finish it. I always died pretty quickly to some dog monster. I never played the full game.

Doom 3 when I was a young teen, although much later it was Amnesia: The Dark Descent that got me more interested in horror games.

Wolfenstein! The lighting and colors alone creeped me out. I could only play a few seconds before I had to stop. But I kept starting it.

Carmageddon and syndicate war 2. They were more 'fun' than wolfenstein but they also had these dark cities.

System shock 2.

Definitely RE for me. I couldn't sleep after the first time I saw a crimson head. The sharks were terrifying too

Slenderman. The OG. I didn't like horror of any type and was always so scared. I was in early college years and chaperoning for a church trip and the two kids in my room were high schoolers I was friends with. They wanted to okay it but we're too scared. Idk what, something about them being too scared to play and making me do it gave me the courage to. Slenderman just looked so goofy in this game. I finally couldn't take it seriously. These two kids were like cowering behind the hotel bed though lol.

Later it was Amnesia: the Dark Descent. It was tough but I got through it. I played it during 4he middle of the day with the lights on lol. I would pause whenever anything scary happened but I got through it!

Festers Quest for NES. It is an Adams Family game where you shoot alien toads with a plunger. It is a definitely, definitely not horror game, haha.

BUT, to fight bosses you have to walk through these totally empty 3D buildings, not knowing what was around the corner. So uneasy.

And when you finally do find the boss BOOM! Almost like a jump scare, similar to the Friday the 13th NES game. Totally terrifying haha.

The first NES Castlevania. Still a classic.

Growing up with the NES, horror games weren't really a thing.

Some were spooky themed, but I doubt they qualify as horror by any standard. Like Castlevania, Ghost & Goblins and such.

The first real horror game I remember playing was Phantasmagoria. But I was a teen at that point, so it's not really from my childhood.

Edit: Remembered my actual first horror game.

I loved Resident Evil but it was the third one that really got me, with the havoc in the streets and the scare where you realize Nemesis can literally chase you from room-to-room and/or show up literally anywhere at any time.

Phantasmagoria.

No, not the more recent VR Game, Phasmaphobia. Phantasmagoria was a DOS PnC adventure game that absolutely scared the shit out of me when I was 9.

Resident Evil 1. I saw bits and pieces of my older brother playing it on the PS1, but was too scared to watch very long. I remember the iconic opening up to the zombie looking over its shoulder and then standing up right in front of you.

I rented it years later for the Gamecube and tried to play it while my little brother watched. I was playing super slowly and wasting all my ammo on every zombie because I was so scared. I remember one part vividly, I was in the long hallway where you pick up the arrowhead and theres a zombie just around the corner. I could hear the zombie so I baited him down the hallway so I could shoot him from a distance. I started shooting when he was off-camera and coming towards me, and when he appeared at the bottom of the screen and his head rotting head being very large in the perpective, I said "woah look at his head" at the exact moment before I got a headshot and the zombies head exploded. Me and my brother were really shocked, so I just paused and quit out. That was enough resident evil for me.

More years later I got resident evil for the DS for cheap at EB games and it became the first game I ever beat repeatedly for different endings and faster times, eventually leading me to now say that horror is my favorite genre.

Also, I never got into Silent Hill as a kid but since playing them in recent years I think they perfectly encapsulate my love for that age of gaming and survival horror in general.

And The Evil Within 1 is the best survival-horror action game ever made. In all its extreme jankiness and difficulty. I did a challenge run of no keys, no upgrades, no cheese in the cheese spots, single segment, no dlcs items, AKUMU difficulty and got 5 deaths. Shit is hard.

Fallout 3 isn't a horror game but man that atmosphere is crazy. I remember one of the very first missions has you go to galaxy news radio from the first settlement, megaton to talk to the DJ. It's a really long journey through subway tunnels and ruined DC streets. The wasteland is pretty horrific and lots of enemies are disgusting and almost disturbing to look at.

As much as Bethesda gets shit for that game, they did an amazing job converting the atmosphere from the first two games into a 3D world.

Uff, hard to say, a lot of the ones comented before applied to me.

As old pc gamer still missing one of the most influent scariest games. Alone in the dark... when you have to deal with the monsters added to frustration of bad controls...

Also dark seed, with all those HR Gigger stuff...

The Penumbra games scared the shit out of me

It was a little later than 'childhood' because I didn't really get into gaming until I was in college, but I would have to say Outlast was my foundation when it came to horror games. I had so much fun playing it over and over, and I still revisit to this day, even through I know it like the back of my hand.
Oddly enough, because I hold Outlast in such high regard, it's kinda of difficult for me to play walking sim-esque horror games that I truly enjoy because I have yet to find one that give me the same sense of satisfaction while playing it (the only exception being the first two Amnesia games).

My childhood originally consisted of the SNES and N64, but I mostly remember things from the N64. I don't recall a lot of true horror games for the platform. There was Resident Evil 2, but the scariest things I remember were specific areas of Ocarina of Time such as the shadow temple or beneath the well.

F.E.A.R.

Animal Crossing and the crushing weight of mortgages

Parasite Eve and Silent Hill 1. I became a big Silent Hill fan and then eventually came to play and enjoy some of the Resident Evil series.

Resident Evil 1 and 2 were the games that I always went over to a friend's place to play, and when Resident Evil 3 came out I got my own copy, and it felt much more like "my game".

Those, plus the original Silent Hill games (1 and 2) really helped define my taste in games, and they've got something I feel even the more recent throwback Survival Horror games don't have, in that they, and the original Alone in the Dark, shared some DNA with the old Point and Click adventure games, like Monkey Island, and Myst. Puzzles based on collecting things, and combining or using things on or with other things, often in mind-bending, nonsensical ways.

The Spencer Mansion, RPD Station, Raccoon City, and Silent Hill were all big explorable areas that opened up as you progressed, and you really got to know them. Games these days feel like they're scared of being accused of "backtracking", so you never spend long enough in any one area to really get to know it.

I had played other horror games before it but the first one I became obsessed with was Resident Evil 4. I think I mostly just enjoy survival horror type games for the challenge, because other horror games have never really held much of an interest to me unless they have some kind of survival aspect.

What do you mean by formative horror? A horror game that had ultimately planted your interest in the horror genre?

Phantasmagoria by Sierra Online.

Eternal Darkness for the Gamecube. Got me more into Lovecraftian horror and horror in general.

Silent Hill 2 on ps2

F.E.A.R. and Penumbra