This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Grand Theft Auto IV
The abandoned Sprunk Factory; a moan heard occasionally when you fire your gun gave rise to rumors of the place being inhabited by a ghost. It's been chalked up to either homeless people in and around the factory or the bouncer at the nearby Honkers, but that doesn't change that the place is just plain spooky (especially at night) due to a heavy dose of Nothing Is Scarier.
The building across the street from the Bohan safehouse have to be one of the creepier places in Liberty City. It may be the weird writing on the walls (such as graffiti saying "Welcome to Hell"), or the distinct lack of human life in there, since pretty much every other apartment in the game has people hanging around in the halls. It's odd you can even enter the building in the first place when there's seemingly no purpose for it. Whatever the reason, the deeper you explore into the building, the more you feel like you'd be safer with your assault rifle/shotgun/RPG out. Even though the building is completely vacant, you may find yourself fearing that something is in there and that your military-grade arsenel won't protect you this time. That's right, this building is the physical embodiment of Empty Room Psych.
There are a few other locations like this. The tall + shaped apartment block near where Elizabeta lives is many floors of empty corridors, and eventually the stairs are blocked off, although there is another way up from this point, however. Once you reach a certain floor you will be running for the roof, which luckily you can escape onto.
There's also a small bit of horror which might have been put in deliberately. Across the hallway from Dwayne's apartment there is another apartment you can go into. The walls are brown and cracked like in some of the drug dens, but what makes this one particularly creepy is if you go back into the bedroom, lying on the bed there is a framed photo of a police officer. The frame is cracked and this immediately makes you think not only was this police officer killed but they came after his family, who deserted their apartment or worse.
An optional police mission has you going into this same apartment, where your target for that mission can be found... blitzed on drugs and not even aware of your presence (in sharp contrast with the rest of said missions which usually have your target shooting at you with everything they've got). Despite this, you're still expected to kill this person. In context it's one of the most brutal killings you'll perform as part of a mission, simply because your target is so helpless.
EddieLow, despite being easily killed (as he's going up against a former soldier now "problem solver") was funny at some points and absolutely horrifying at other points, such as when he has Niko take him to a place to drop off what is not so subtly implied to be the head of one of his victims, or when he decides he wants to hear some Algonquin screams tonight now that he's heard enough Alderney screams. The peak of the fear is reached when he's losing his temper just before he attacks Niko.
Eddie:Not COOL!? You say Eddie's not cool? I don't fit in with the "In-Crowd?" Well Mrs. Smith, Eddie's taken your star son, your prized little quarterback, and FUCKED HIM IN THE ASS, and then tied him up, strangled him into knots, and your daughter? Your pretty little daughter Mrs. Abrahams? Eddie's ripped out her intestines just to see if he could feel anything, and you know what? He couldn't...h-he couldn't...
And then there is Jeff. At first it's pretty funny. Jeff's a man who thinks his wife is having an affair. Seems legit, until you actually follow her to her destination. Turns out, she just wants to talk to this guy about her husband, who wants to install a tracking chip at the base of her skull which may paralyze her. 'Course, the guy is only half listening and does want an affair. So, you take a picture, he rants and raves, job done and a couple of hundred dollars. Then Jeff calls you again. He's murdered her. Stabbed her "fifty fucking times" and is so crazed he nearly shoots her corpse. Then reveals that she and him have a son. It's hard not to feel like you had a hand in murdering this truly innocent woman.
The crackdens in Algonquin near where playboy X/Dwayne/The Safehouse is is, quite frankly, terrifying. They're the plus buildings on the far side and they're filled with empty rooms, gangs, bloody pillows and mattresses and hookers.
Niko's backstory is pretty horrifying, he talks about how he went into a church and saw fifty dead children with their hands chopped off and their throats slit.
During the mission "Taking In the Trash", one of the Pegorino soldiers you're working with tells a story about Ray Boccino's temper that's downright chilling.
Niko: He has a temper?
Luca: Are you fuckin' kidding me? The manager of one of his waste depots was holding out on profits a couple a years back. Ray fed him to a dump truck. There was this point where the sound of his screams stopped, and all you could hear was his bones crushin', then the pop of his skull goin'. I nearly lost my lunch.
In the game files, several unused death sound files are found, and they are ominous sounding versions of the main theme.