Many of the corpses you come across are creepy. Among them is Agent Daniels's, which is burned and mutilated. Even worse is that there's a speakerphone that's connected through his body and is propped up in his mouth. Yuck.
And that's not to mention the mass grave you fall into filled with corpses or the countless people seen hanged on the street lights and billboards.
The aftermath of the white phosphorus incident. Smoke everywhere (which, by the way, is toxic), horribly burned bodies, the few survivors whimpering or shrieking in agony and often missing limbs, the pen full of dead civilians — including women and children — and the knowledge that it's all your fault. Imagine the AC130 missions, but with chemical weapons, and played completely straight on how the damage actually is, rather than playing it for "awesome" against pre-rendered, unchanging backgrounds.
Made even worse by how completely impersonal the actual bombing is. You don't even get to look directly at what you're doing until it's all over.
Walker finding Konrad's decaying corpse. Not only is the sight of this dead body disturbing in and of itself but the deeper psychological revelations that come with it basically invalidate everything Walker had been working up to in that one moment. The Despair Event Horizon comes and it hits hard.
Some of the graffiti found throughout the city can be unsettling, whether it's actual pictures or just scrawled writing. These are the thoughts and feelings of the survivors, so when you find pictures of violence and suicide, artwork bordering on Body Horror, and one piece of graffiti that simply reads "DUBAI DIED SCREAMING", you can guess what the people left here are going through.
Early on, just before you fight the 33rd for the first time, you pass through an abandoned civilian campsite. On the wall at one point, there are several childish drawings. Mostly they consist of things like US helicopters being struck down by lightning, but one of them appears to depict the rape of a woman by US troops, next to some trees filled with hanging bodies.
The way that in the ending Konrad gives you a simple choice - shoot him or he'll shoot you - is so menacing in how deliberate and definite he is about the choice. Walker is trying his best to maintain his composure and find some way to reason his way out of the situation but Konrad continues his countdown regardless. Konrad's cold and mechanical thought process has already been decided, either he suffers judgement at Walker's own hands or Walker dies when he pulls the trigger; and then when he finally finishes his countdown, the tone of voice he uses sounds evil, like that of a true monster. The whole exchange is very terrifying.
Of course, this makes perfect sense. Walker is aware of the atrocities he's commited, and is scared shitless of what he's become and the punishment he'll receive, but he still feels like he should be punished for it. Since Konrad is the personification of Walker's guilt, self loathing and desire for judgement, he would appear to be warm and talkative one moment, yet cold, ruthless and utterly horrific the next. Compare the hallucinatory Konrad before and after discovering Konrad's body. Konrad is essentially the Spec Ops version of Pyramid Head.
The gradual progress of Walker's Sanity Slippage over the course of the game is terrifying in its own right. Watching the cool, collected, mild-mannered captain slowly transform into a gung-ho, vicious, all-American psychopath over the course of just two days is quite horrifying to behold. Nolan North's performance really sells the transition: it's unsettling when you hear Walker yell "Kill is fucking confirmed!" for the first time, but even more so when you realize it's the same man who calmly informed his team "Target neutralized" at the beginning of the game.
What makes it even worse is that initially Walker comes off as a character similar to Nathan Drake from the Uncharted series. A more or less good guy who tries his best to do the right thing, but his wishes to be that kind of person are quickly deconstructed. Walker is basically what Nathan Drake would be like if someone broke his spirit and his mind and warped his moral compass. The idea of a good person being broken down like that is disquieting. Especially when you think about Walker's motivations and realize that they were never less than sympathetic. He wanted to do what was right. The idea that one can have completely, unambiguously noble goals and motivations and still end up becoming a Villain Protagonist is a rather bleak one indeed, and almost a little heartbreaking.
YMMV on this one, but it's a good example of Fridge Horror. When Walker assists Riggs in stealing the tanker trucks full of drinking water, Konrad berates him for assisting the CIA in their cover-up and spelling the doom of Dubai's remaining survivors. But as you may know from the end of the game, Konrad is just a voice in Walker's head and Riggs never reveals his true intentions until the trucks crash. This means that Walker recognized at some level that Riggs was orchestrating the death of thousands of people, but convinced himself to go along with the plan anyway.
The slow, horrible reveal that Walker, not Konrad, is the true villain of the game. Walker massacred hundreds of US soldiers who were acting purely in self defense. Walker murdered dozens of civilians with white phosphorus. Walker destroyed Dubai's only source of water, dooming thousands to a slow, agonizing death. Walker knowingly led his comrades to their deaths in a futile attempt to convince himself he was actually a hero.
The title screen opens with some rather striking imagery: a sniper lounging under a tattered, upside-down American flag fluttering on the top of a skyscraper overlooking the sand-covered wasteland of Dubai, set to the music of Jimi Hendrix's rendition of The Star-Spangled Banner. A bit unnerving, but not too bad on its own. However, the sniper changes positions as you progress through the campaign, occasionally looking through binoculars or aiming at a target we can't see. The flag changes too, becoming increasingly torn as the game goes on. For the last level, we see a pair of ravens picking bits of flesh from his corpse against the backdrop of a night sky as fires rage in and on the buildings.
And once you've finished the game and played through the epilouge, the snipers corpse is gone, with only a bloodstain and some raven feathers to show he was ever there. The pole that the flag was on has fallen on the exact spot where the snipers body was, and the tattered strips that were once the flag is wrapped around the broken bundle of sticks. The buildings in the background are broken, with one almost cut in half and ready to fall, and the whole picture has barely any colour. It's a very effective case of Nothing Is Scarier, as it makes you wonder just what the hell happened here.
A personal one players can set up for themselves is the lynch mob scene. You just ran through hell, desperate to make sense of things you've seen, rationalize everything you've done and now you are separated from your team. After reuniting with Adams, you hear Lugo over the radio is in danger of being found by the 33rd. Walker orders him to find a place to hide before they come find him, but the unspeakable happens. Lugo starts to panic and inform Walker and Adams he has been found. There's a violent scuffle heard over the radio and the last thing you hear is Lugo screaming in fear and begging for mercy. By the time you arrive, you find your fallen comrade hung on a rope by an angry mob of civilians. You shoot down the rope and desperately try to revive your ally while Adams threatens the mob to stay clear. When it is clear Lugo has died, you are left with the civilians wanting your blood, Adams literally begging you to give the order to gun them down, and your own burning rage at the unjust punishment handed down upon Lugo that you deserved, not him. Just you try to contain your anger with your finger hovering over that trigger, then after you calm down much later, ask yourself if you really did the right thing.
More generally, replaying the game after an initial playthrough and noticing little details such as these (along with others such as Konrad's face appearing on billboards) will make the player come to an unsettling conclusion: Walker was always insane, teetering on the brink of a complete mental breakdown; he was just better at hiding it in the earlier parts of the game.
The two Snicket Warning Labels in the game are curiously unsettling in a Nothing Is Scarier kind of way. Delta are approaching Dubai, readying their equipment, and what's the first thing they see? A big red STOP sign, pointing directly at the player. The idea of a game telling you to stop playing it is weird enough; after Konrad's line at the very end of the game it becomes downright unnerving:
Konrad: None of this would have happened if you'd just stopped.
Riggs' increasingly desperate cries if you don't Mercy Kill him after he crashes the water trucks. Sure, he had it coming, but it's still disturbing as hell.
Most of the trailers for the game misrepresent it (probably deliberately) as a generic Modern Warfare clone, but the "Journey" trailer gives a much more accurate sense of the game's tone and themes, with much of the horrific imagery from the game hinted at, distorted Semper Fi-esque phrases ("STRENGTH", "DUTY", "HONOR", "FREEDOM", "ME") flashing on billboard screens in a manner reminiscent of the montage sequence from The Parallax View, and a creepy, tinnitus-like tone ever rising in pitch throughout, all building up to a terrifyingly evocative clip of a shell-shocked Walker with a Thousand-Yard Stare staring at the Burj Khalifa engulfed in flames.
In the worst ending, Walker slaughters the Deltas who arrived to his rescue, picks up a communicator and addresses whoever is on the receiving side: "Gentlemen, welcome to Dubai" before arming himself and heading back into the city. God help any survivors...
Walker's hallucination with the heavy soldier who seems to be Flash Stepping from side to side every time the light "goes out": he walks towards you, shooting and shifting position, and you almost panic because you have no idea whether it's real or a hallucination, whether there's just one enemy or two, and the whole time, Adams and Lugo are under fire waiting for rescue...
Unrelated to any War Is Hell psychology, but whenever the oryxes appear, it feels so unreal, it's almost creepy. So you wander through the very human tragedy of the devastated Dubai, when suddenly, these weird antelopes appear seemingly out of nowhere and start running—and you're not at all sure whether they're really there (they can't be, can they?) or Walker's seeing things again.