For me it was Dead Space 2 when I was 12-ish. For reference, at this point the most gruesome/gorey/violent media I was exposed to was the Halo 3 Flood levels and the original 2 Alien movies.
I had way too much fun playing it to be traumatized by it at the time, although when i was old enough to understand the horror of the whole “your memories and experience becoming food for a god-like being that has absolutely zero respect for your existance”, that did inform my perspective of other media such as Evangelion or Childhood’s end when I watched them for the 1st time.
What was your equivalent to this? I’ve heard the Resident Evil games are quite common for this but I want to hear your perspective.
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!