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.
Fun fact - that 'puzzle' has its difficulty set by your processor's speed. The game uses a set amount of time to determine the best move for the computer, and plays the best it's got after that time. On slower processors of the time, it would only be able to calculate so many options before needing to come to a decision, but because it didn't account for better hardware, the computer can make the best move every single time, causing it to be unwinnable even if the human player also plays perfectly.