S.T.A.L.K.E.R.: the shit-scary atmosphere of the underground levels, creeping through so slowly for fear of what could be behind the next corner. Or any time you get jumped by a blood sucker out of nowhere.
One time I was just leaving a bandit base after a long, drawn-out fight, carrying the spoils of victory and going round all the dead bodies I could find (marked with grey dots on the radar) when I noticed there was dead body in a little 2-storey out-building that I hadn't looted yet. So I go in, climb the stairs, go into the little box room where the radar dot is and... there's a skeleton. Looks like he's been dead for some time. Immediately my brain is shouting "it's a trap!" and not two seconds later I hear that unforgettable noise like no other: the growl of a bloodsucker. "The son-of-a-whore tricked me!" Scared out of my wits and veins full of adrenaline I spin round and pull out my AK just in time to drop the monstrosity, and only lost about half my health.
The first time I saw one in game was in the Wild Territory at night. Just beyond the first building you go through after leaving Bar, I glimpsed a tall, gangly figure walking around. Didn't see much detail, just that it was obviously humanoid, but not human. I stood still and it walked on without seeing me. Maaan.
The second time was in Wild Territory again, this time coming back from Yantar and I'd just cleaned out the 3- or 4-storey half-constructed building where the bandits like to hang out. From the top I could see it wandering around down below. It would uncloak for a couple of seconds, see me, then cloak again and run around the railway buildings for a minute or two. It didn't understand stairs, so I was safe up there and I tried picking it off with my AK but it was hopeless; I knew I would have to go down and face it at ground level. A similar situation happened in Cordon, at the abandoned mill or whatever that building is, just south of the railway, I was on the roof and this bloodsucker was running around down below. They have this knack of always coming at you from behind. So then you spin around, but somehow they know to then come at you from the direction you had been facing originally
And underground at Agroprom, there's more of them the second time you're there. I was in a position in a corridor where they could come at me from the front or from behind, and could hear one walking close by, breathing heavily as they do, so I figured the best thing was to wait for it to come to me. So I stand there, every few seconds I turn 180 degrees in case it's coming from the other direction. Then suddenly I turn and it's there. Right there in the corridor. It sees me. It starts running. I wait until I can see the whites of its eyes to unload my pump-action shotgun into it
I love when you meet different monsters for the first time, like the Controller or the Poltergeist. And then at the brain scorcher when it really starts fucking with your head
Also whenever I see someone wearing a welding mask, on TV or whatever, I get a little spine chill reminding me of Yahtzee's Chzo series.