This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / BioShock
The beginning of the game. It seems innocent enough. You're on a plane, reading a letter. Then all of a sudden the screen goes black. There's the sound of a plane going down... and screaming. Lots of screaming. Next thing you know you're underwater, you force your way to the surface... among the shattered remains of your plane. Later, you find out who was responsible for the plane crash: It was YOU.
Right when you first enter Rapture, a Splicer just... guts your would-be rescuer, and all you can see are vague outlines of what's going on, accompanied by a horrible squishy ripping sound and the victim's gurgling. You can't even get a good look at the corpse to calm yourself.
"Is it someone new?..." After seeing you, the Spider Splicer jumps up on top of the bathysphere you're in, you hear a thump, and then a screech and sparks as it starts cutting through the top, the whole thing rocking—and the door just won't open. Even more terrifying, since the entire sequence happens after the HUD comes on, but before you're given any instructions on how to defend yourself. In this case, it flips even expectations on you as you now expect to fight that... thing outside, but you have no weapons or items to help, and it just butchered that dude... "Take a deep breath, and step out of the Bathysphere."
And what's the very first thing you see after that? Piles of abandoned luggage, picket signs that say "Rapture is dead!" "Ryan doesn't own us!" "We're not your property!" and "Let it end! Let Us Ascend!" scattered all over, and finally, you come to an official looking notice pinned to the wall that reads "Attention! All Bathysphere travel is now denied." It sends chills up your spine when you realize what it means, too. Ryan is in so much denial about how secret Rapture is, he traps the population inside it in a vain attempt to hold onto a dead idea.
The Lighthouse, which is more than a little creepy already. You just barely escape the plane crash in the middle of nowhere, and you see this big creepy tower just standing there in the middle of the ocean. You go in, and the first thing you see is this big gold statue, and big red banners with propaganda all over them. A very strong Fascist vibe just from that, and then you go down in the Bathysphere, and he treats you to a film containing an equally disturbing speech (something about "the great not being held back by the small", and the way he says it) and with similarly fascistic imagery (Look at all the old Nazi, or Soviet propaganda and you can see the exact same kind of imagery, with the barely human looking farmer, the big political symbols in the sky attacking him). Also the sound the lights in the Lighthouse make when they come on is eerie. In fact, the brief Scenery Porn of you coming up to the city is probably the only break in the entire game.
The lighthouse is spooky as Hell, but what else is Jack gonna do? He has to swim toward the bizarre building or drown. And if he was an avid reader, he'd be downright terrified. Equally creepy is when someone on the surface discovers it too.
Ever thought about the Splicers being kind of weak? About how a quick stun and one well-aimed wallop with the wrench to the head takes a lot of them out? Welcome to real life.
Also, a lot of the people coming to Rapture were actors, poets and musicians. No wonder they're lousy fighters. But there sure are a lot of them...
And when Jack's appearance is revealed through his audio log, the last moment of a splicer's life was a circus's strongman swinging a wrench with nothing to stop him.
The voice modifying machine when being converted into a Big Daddy. Looks painful, and the fact that screaming would only intensify the pain. Heck, the entire Big Daddy conversion process qualifies.
Then how does Jack make human like sounds after the conversion?
The process goes something like this: Foul-smelling pheromones are applied to the candidate, and the voice box is modified. Then the skin and organs are removed and grafted inside a huge diving suit. Meanwhile, the candidate is immersed in a yellow substance that keeps them alive, but reduces their mental capabilities. They're then taken out and sealed inside the suit. Gene splicing and plasmids give them enhanced strength and agility, while the suit maintains life support, protection, and allows them to survive in the depths of the ocean. They no longer have any sense of free will.
The Splicers in general are pretty creepy, but especially the Spider Splicers. The first encounter you have with the Houdini Splicers is also particularly terrifying.
If you thought the splicers were too easy by the middle of the game, good news! About halfway in, the splicers have learned how to play dead. Have fun checking every single corpse.
Take all the Biblical references from the Waders and think about them even more. This is a society that was built around the idea of man prospering by his own hand, without an eye (or a heart) for God. Andrew Ryan had cut off contact with the surface to prevent his city from being "contaminated" by outside influence. Early on in the game (the start of Neptune's Bounty), you see a man who was hung up and "crucified" by way of firing squad. There are stacks of Bibles beneath him. As the game goes on, you hear more about the idea of valuing one's own self above everyone and everything else, of seeking as many carnal pleasures as possible ... and you see box after box after box after box of smuggled Bibles, in some cases literally littering the floor. Now consider the meaning of those creepy-sounding hymns and verses. What these people did to their bodies was only one aspect of their torment.
"Jesus loves me, this I know. For the Bible tells me so..."
"We thought we could hide from the light down here! But you can't! It's everywhere! Oh father, why have you forsaken me!?"
"He sees everything sees everything sees everything sees everything sees everything..."
"Go ahead, run! That's all your kind is good for, go, RUN! OH PLEASE DON'T LEAVE MEEEE!" and the young man's "OKAY... I DID IT! YOU HEAR ME, I DID IT! CAN I GO NOW!?" spoken after he kills you.
"I observe all his commandments... I observe all his commandments... I OBSERVE ALL HIS COMMANDMENTS! * starts sobbing* I OBSERVE ALL HIS COMMANDMENTS! HIS COMMANDMENTS!
Oh God, Dr. Grossman, oh God. "I don't want to hurt you, I just want to see what's inside!"
In addition to his morbid curiosity, the Doctor's deathly afraid of germs. "I like the prestige, but I don't like the germs. The germs, they-they get under your nails, they crawl around at night." His is a world where Death is everywhere, writhing and squirming both without and within, infecting wherever it can take hold.
Enemies reflect damage they've taken, which means if you tend to use the fire plasmid or chemical thrower, all the dead splicers are grotesquely burned.
There's one infamous encounter in the dentist's office, in the Medical Pavilion. In the dentist's office, you break a window, destroy a turret, and walk towards the dentist's chair. Suddenly, a thick white fog appears, you can hear someone running nearby and a THUD sound, and when your vision clears there's a corpse sitting in the previously empty chair. Just past it there's a table with goodies on it. When you get there, the fog starts up again. When it clears, you pick up the goodies, turn around, and there's a doctor right in your face. Thankfully, he won't attack until you do.
Similar to the above, there's a part in Arcadia when you approach a desk and the lights flicker, only for them to come back on and have the player see a shadow on the wall and realize that the splicer is standing right behind you.
The Little Sisters, not just encountering them, but harvesting them. Little girls with muddled skin, dirty clothes and hair, Glowing Eyes of Doom and warped voices, who tag along with Demonic Spiders whose Berserk Button is you upsetting them. Yet, they are extremely Tragic Monsters (as are the Big Daddies, once you learn more about them) whose origin stories are full of Parental Abandonment and Moral Event Horizons. But even when you feel sympathetic for them and want to save them (and you most likely will), you have to endure a short cutscene where they pop up in your face, letting you bask in their full Uncanny Valley horror as the player character physically struggles to use his Little Sister reversal power on them because they're brainwashed to only trust Big Daddies and they don't know you're trying to save them. Of course, you get an even more horrifying cutscene when you harvest them. Someone else clearly felt this way, too, because their appearance is toned down in the sequel, and the Rescue sequence there has them happy and calm the whole time (though this is justified, as you're a Big Daddy yourself in that game).
Those moments when then you find out the Little Sister can occasionally see what's actually going on, for example when they shout "Your faces are melted!" at attacking Splicers.
Now consider that Splicers (and before the Fall, regular citizens of Rapture) are actively hunting and killing Little Sisters for the ADAM in their bodies. Never mind that before killing a Little Sister, you first have to kill her Protector, and she'll probably witness the whole thing. Never mind that by attacking her you've snapped her out of the hallucination that lets her ignore what she's actually doing. Little Sisters are practically indestructible, able to regenerate broken bones in a matter of seconds. What kind of ungodly damage are you going to have to inflict on one of those little girls in order to actually kill her? Quoth Diane McClintock:
"It was something awful what they had to do to that little girl to get the ADAM [...]"
And if you think their appearance is creepy, you should be thankful they didn't went with THIS◊ design for the final product.
Big Daddies are Gentle Giants and absolutely harmless, despite being creepy-looking, walking with very heavy footsteps, and being followed by Little Sisters. Unlike most enemies in the game, they won't attack you even if you get right up in their faces. On the other hand, if you attack one, it goes completely ballistic and throws itself at you really, really fast. It won't stop until you clear out of there (or kill it), and next time you see it, it's back to calm. A Berserk Button indeed.
The introduction of the Big Daddy. You see a Little Sister without a Big Daddy, gathering ADAM from a corpse. A Splicer jumps down and starts to menacingly approach her. She lets out a very loud shriek that makes him hesitate. Then you hear a roar and a Big Daddy leaps down, facing the Splicer and keeping it away from the Sister. The Splicer shoots at it, to no avail. Then the Bouncer lunges, there's a loud VREEEEEN noise, an agonizing shriek, and a spray of blood on the window you're watching out of. And that's not all - it slams the Splicer into the nearest wall, drills it for a second, then SLAMS it against the window. Once, twice, thrice - and on the third time, it smashes through the window. The unbreakable, bullet-proof window. Which is a pretty good indicator of just how strong the Big Daddies really are.
If you get close to the Little Sister, they'll push the little girl behind them, and start up that giant drill. Especially terrifying after you've seen how fast Bouncers can move, and what they can do to people with that drill. And the pushing behind... is it because of the fear that there's something like a human mind in that armored shell? That to the terrified Little Sister, you're the monster and Mr. Bubbles is the good guy? Or is it just the completely natural terror that comes along with realizing that pushing Little Sister to safety will immediately lead into mutilating your body with that drill/rivet gun? Probably a little bit of both, mostly the former. Like Shadow of the Colossus before it, this game seems to subvert traditional ideas about video game bosses. Big Daddies seem to be one of the few "honorable" characters (or character sets) in the BioShock universe, but if you don't kill them, you don't get ADAM, and thus you have a harder time surviving. Though that would make an interestingSelf-Imposed Challenge, because you (probably) only have to defeat one for the sake of story.
Everytime you hear those clanging footsteps, followed by a Little Sister's voice, it fills you with dread. You know fighting the Big Daddy will end with you badly hurt, low on ammo and EVE, no matter how much you've upgraded your weapons and Plasmids. But that's not the worst part. The worst part is knowing that attacking him is absolutely necessary.
The audio diaries... The fact that you hear and know what's going on without seeing it, and therefore forces you to fill in what's happening in your mind has a creepy 'radio-drama' feel to it: (Ex: "Doctor! Stop cutting!" or "Break her neck for me, would you kindly?")
One of the many Plasmids you can pick up allows you to summon a swarm of bees to distract your enemies and deal some damage over time. These bees erupt from your arm in a fairly gruesome way. To quote the wiki:
Having to use those oh-so-sterile needles. Bonus for getting fear of needles and fear of disease at the same time.
Try waking up in a Vita Chamber, miles from the actual fight, and finding a Splicer right in front of it. The Splicer said, "Do you know what we do to Judases!?"
Occasionally if you shoot off a splicer's mask point blank, they will scream. Combine that with their horribly mutilated faces and chances are you'll be screaming along as well.
The abandoned CRT Monitors scattered throughout Rapture's homes and business. "PLEASE STAND BY"... FOREVER.
Early on in the game, you come across a Splicer leaning over a baby carriage, talking about how she wishes it was like the old days, when he was warm and moved and cried... and if you get too close, she shrieks "Baby and me, BABY AND ME!" and tries to bludgeon you to death. Made somehow worse when you discover there's nothing in the carriage but a revolver.
What Atlas says after the encounter doesn't help either. "Babies strangled in cribs...".
The Medical Pavilion, all of the cutout faces on the wall. It may have something to do with the fact that patchwork zombies sink to the very bottom of the Uncanny Valley, or a personal fear of disfigurement. The boss for that level being all "Why are they all ugly -stab- !" didn't help much, either.
The Twilight Fields funeral home. Yes, a splicer jumps out from behind a coffin, but that's not the scary part: it's when you enter the morgue. Upon entering, you can see a few cabinet sort-of things in front of you and a corpse. Over to the left is some water. Going into the water will cause a body to float down-stream towards you. On the wall ahead of you, you can see the shadow of a doctor cutting up a cadaver. There's a wall blocking you from seeing him, however. As you approach, the lights go off for around 3 seconds. And then the lights come back on, and the shadow of the doctor is gone. After going over to the corpse, you'll notice one of the 'cabinets' closing and the music takes a very scary turn. Once you attempt to leave, however, the doctor will jump out of one of the cabinets and likely scare the living crap out of you.
The corpse lying on the table. Its head is twisted and it's staring straight at you, jaw agape. The main morgue is horrific as well, you can still hear the strange, soft organ music coming from the funeral home and the water flowing from the tables where corpses are lying is green.
There is a female Splicer crying over a table. Look at what is on the table. It is a three-foot long coffin. A baby's coffin.
The shotgun's just there on the floor in a spotlight, all innocent, and when you pick it up the freaking lights go out. And then the screams start, and you fire blindly into the darkness, and when a light flickers for just a moment you see a horde of splicers racing around you, leaping at you as you pray one of them will eat buckshot to the face. The lights don't come on until everything is dead, and by then you've spent every shell the shotgun came with in panic. Then it becomes your best damn friend in the world as the only actual gun that shoots lightning.
In the Haephestus level, there's an office with lockers in it. Since you've been searching everything so far, obviously you search them too. From one, a corpse falls out. By now you've seen all that death, but you stare for several seconds. Then you search the corpse.
The part before you go to the medical pavilion. Andrew Ryan talking to you, and then an army of splicers is banging on the door obviously baying for blood, the door won't open, and then the glass starts to crack...
There's the recording 'Not What She Wanted,' in which Steinman conducts what is presumably his first unnecessary surgery, whistling away.
Nurse: Uh, doctor, she's not booked for a face lift ... Doctor ... stop cutting ... DOCTOR, STOP CUTTING! GET ME THE CHIEF OF SURGERY! GET ME THE CHIEF OF SURGERY NOW!
Ghost: *pounding on closed door* You promised me pretty, Steinman! YOU PROMISED ME PRETTY! Now look at me! LOOK AT ME!
Gets worse when you think about it - who did you just hear talking about how 'pretty' Steinman was going to make her? None other than Diane McClintock, Ryan's ex, who was injured in the New Year's Attacks. She says that Steinman did his best...
And as soon as you go through that door, you're greeted by three portraits, which have dashed outlines and large pairs of scissors angled over certain parts of their faces, copious amounts of blood everywhere, and on the floor... "Above all, do no harm." Even worse, if you position yourself half behind a column while looking at one of the pictures (of a woman looking to the right), the picture changes and she's looking right at you.
Due to the founding principles of Rapture, Dr. Steinman wouldn't have been bound by the Hippocratic Oath anyways. He is either specifically calling attention to the fact he is going out of his way to violate it or so screwed up that he legitimately thinks what he is doing is helping.
"I had lunch with the goddess today..." People were still going to this guy for surgery even when he was so clearly insane that he hallucinated lunch appointments with the Goddess Aphrodite. How badly did Rapture function by the end? That badly. Made even worse in the novel where it's revealed he had these visions before ADAM was discovered.
Early on, in the second level of the game, you come across a recording of the lamentations of a mother, desperately looking for her daughter, terrified that she has to be taken away "to save Rapture". You can probably guess what happened to the daughter... right? Later on, you come across a 2nd recording, which confirms the sad fact: this woman's daughter has been converted into a Little Sister. If you think that's bad, it gets even worse: you find the recording on the remains of the mother; she and her husband killed themselves by overdosing on pills, died in each others' arms on their bed, with a picture of their dead daughter right next to their corpses... Doesn't help that the lights go out after the audio diary finishes.
In the Fisheries you discover a corpse handcuffed to a pipe, hanging from the cuffs with electrodes tied to his body. The diary nearby gives you the information that Ryan was ordering men such as this one tortured for information and to intimidate his competitors.
Peach Wilkins is very creepy. Aside from the paranoia, he seemed fairly sane, and later on, it turned out he was right. His whole aura and his mannerisms were rather creepy as well, as was his whole freezer area. And his boss fight is hard as until you remember Telekinesis.
In Fort Frolic, there are very lifelike plaster sculptures, often with terrified expressions on their faces. If you shoot them, they bleed. It's best not to think about the implications of that too much.
If you go into the room with the three safes beside the main entrance to the Fleet Hall, the man at the end of the table has had his wrists slit. Also, some of the plasters have had their throats slit, like Sander made them and then put them out of their misery. The only idea worse than this is the idea that the ones that aren't already bleeding died in the plaster. And knowing Sander Cohen, he probably gave a quick death to those people, not because of some sense of mercy, but because they were squirming too much.
Anything relating to Cohen really will probably make someone void themselves. "The Wild Bunny" recording. "I want to take the ears off but I can't! It's my curse! It's my fucking curse! I want to take the ears off! Please! Take them off! Please!" Cohen, and Fort Frolic, the level he calls home, are products of the same mind as The Shalebridge Cradle from Thief.
Go ahead. Just try and take the ears off.
One room contains nothing but a few safes and three of Cohen's plaster 'statues' sitting at a dinner table. One is a man, the other is a woman, the third is a little girl. It gets even worse though, once you realize it might be a Little Sister, which becomes more apparent when you realize that it's the only statue that doesn't bleed. Unable to move, unable to speak, unable to die...
In the clothes store in the back there is a table and door leading to another room, and the door opens by itself and there sits a statue JUST STARING AT YOU. It seems that the minimal distance required for the door to open is programmed to be a little longer compared to other doors.
Fort Frolic's basement? In one of the stores selling spirits, you proceed past two flanking rows of rabbit-masked dancer statues to see another statue standing crying next to a locked door. Find the switch behind the counter to open it, and you find a goodie in the room beyond. Turn to leave, and... huh. Was there a statue there earlier? Oh. Roughly half of all the statues in Fort Frolic have suddenly disappeared. And then, you can actually enter the basement. A flooded room with the glass wall and all those mannequins? Yes... they're only mannequins... they can't hurt you... Also, making the spirits store sequence even better is the Soundtrack Dissonance of "How Much is that Doggy in the Window?".
Aside from a statue going from sitting in a corner like it's the victim at the end of the Blair Witch Project to being right behind you when you turn around from your own corner, using that Power to the People machine causes plaster Spider Slicers to just show up periodically and battle you. Some walkthrough experts simply avoid that machine, because the spooks and the hassle just aren't worth it.
The animated plaster Spider Splicers there are so damn scary. They are completely silent. That's right. They can quietly climb along the ceiling and drop down directly in front of/next to/beside you and start attacking. Somehow that's even worse than the same thing with their usual delirious ranting. They are made even scarier if you're familiar with Doctor Who'sWeeping Angels.
Sinclair Spirits has to be the most terrifying place in the game. Something as simple as all those statues disappearing... Sometimes they strike poses in places you've already passed. Release the plaster splicers and then go over to the waterfall under the staircase.
All these things are just surprises, though. There's a more psychological one in that a suitably experienced and mobile FPS veteran will have just, as requested, done a little dance on demand for Sander Cohen, which is a pre-echo of the whole Would You Kindly/FPS-means-But Thou Must theme.
One of the most unsettling parts of the entire level was the gents' toilet in the southern mall. Video game toilets in general are scary, but something about the three Cohen sculptures in there, stuck in unnatural, dance-like poses with black plastic bags over their heads, casting weird, twisted shadows in the flickering light; it's just terrifying.
The tunnel to the ice cave. "I can see your brea~ath!" This one also falls into, thanks to some wonderful stereo mixing that makes this sound like it's being spoken by someone in the room you're sitting in, even if you just have two decent quality speakers.
Cohen has no face. He plastered over his own head and then painted a face on top of it. Enjoy!
If Cohen wasn't shown to be deranged enough, one of the first times you interact with him, he has chained his former follower to a piano that is rigged with explosives and forces him to play Cohen's song perfectly. He doesn't.
Two areas of Fort Frolic (the Atrium and the Poseidon mall) have little ambient lighting, the player's main light source are these spotlights that follow you as you move through the room, tracking your movement. Then you realize that someone must be operating those lights to make sure they always shine on you; Cohen. In Rapture you're always being watched but in Fort Frolic Cohen makes it a point to let you know that he can see your every move.
The damned vending machine in Hephaestus. It's rigged with explosives.
There's one certain hallway. A corpse-strewn corridor is nothing new, right? But every few paces the lights switch off, you hear people rushing around you in the darkness, giggling, and when the lights go back on some of the "corpses" have moved. There are two responses: some players will keep pushing along in cold dread, knowing that at some point the Splicers will tire of their games. Others will get out the Chem Thrower and hose down every body with napalm, just to be sure.
It doesn't make any sense, but it makes it worse that even if you do shoot the bodies lying around, damage doesn't register UNTIL they get up and scare the shit out of you. You can see this if you set some on fire.
The lobby just outside Rapture Central Control, where the corpses of people who turned against Ryan are staked to the pillars, almost like trophies. Of particular note is Bill McDonagh's charred corpse, making you wonder how he died. In the book it was his friend (terrified of Ryan) killing him; he shot him in the head instead of actively crucifying him first.
There are a lot of bodies on that wall... but two pillars don't have bodies on them. One for Atlas and one for you?
WOULD YOU KINDLY? The Arc Words in great red letters written on the wall.
Also, the radio diary right before The Reveal. "Break that puppy's neck - would you kindly..." It makes you feel naked and exposed to the true horrors of the game.
From both an in-universe perspective and a meta-perspective, the horror of "Would you kindly.." hits you hard following Ryan's murder and Atlas contacts you again to stop Rapture from blowing up using those very. Same. Words. From Jack's perspective, he's completely unable to disobey Atlas. From our perspective? The game presents us with only that choice. Forcing us to proceed in only that fashion.
When you finally get to meet Andrew Ryan. Someone mumbling 'A man... chooses... a slave... obeys... OBEY!' through a shattered jaw with half their face a broken mess whilst you pummel them with a golf club is definitely nightmare fuel.
Even though he's supposed to be a legitimate businessman, Ryan keeps corpses of his enemies crucified to posts outside his office. You can search them. Some have Audio diaries on them.
Ryan's video to you is creepy. The brim of his hat is obscuring his eyes, and his voice is emotionless.
And then there's the scene when Atlas reveals his true self and transforms Ryan Industries into Fontaine Futuristics. An unsettling combination of being underwater, more steam coming from tower than a tea kettle, a deranged case of Evil Gloating, and a sharp change to a red, ominous logo not only drives home the horrors, but also how badly you've screwed everything up. Not that you really had a choice.
Right at the start of Olympus Heights: CODE YELLOW. Not only do you slowly lose health over time from it, but the description of "telling your brain to tell your heart to stop beating" is just absolutely terrifying.
Possibly the worst part is how slow it works. ("It ain't gonna happen all in one go. Heart's a stubborn muscle.") Every few minutes, Jack lurches, the screen turns a shade of blue, and you hear a loud THUMP on the soundtrack. Then you realize what that means. Every time that happens, Jack has a heart attack.And your health bar is getting shorter.
By the time you get to Point Prometheus, you've got enough weapons and plasmids to not worry about dying anymore. But then you get to the Little Sisters Orphanage, and see that one ghost scene, of a little girl scooting back into a storage closet, sobbing "Please, Dr. Suchong, I don't want to go onto the table!" Two notes: we've never seen a "ghost sequence" from someone still alive, and the closet she was hiding in was piled high with stacks of identical little dresses. You have to wonder about what the failure rate was for the Little Sister conversion.
That's not all. Earlier, in Suchong's Apartment, you actually find the corpses of little girls on a couch.
There comes a point where you stop being afraid of death in this game. That doesn't stop you from being afraid.
When you're with the Little Sister disguised as a Big Daddy at the end. The things she says to you. "Hurry up Mr. Bubbles. Angels are waiting for our kisses."
The creepy noises and moaning, ghostly voices heard walking around in the Artemis Suites and Fontaine's Home For the Poor.
There is a SERIOUSLY scary noise that pops up out of nowhere in these levels. There's nothing worse than exploring a dead silent room and hearing BUUUUUUNHZZZZZZZZT in the atmospheric track.
Said sounds seem to be coming from the fourth floor, which happens to be blocked off. What in God's name is up there?
The "Bad" ending of the game. You take over Rapture, sending an army of Splicers to the surface and killing the crew of a nuclear sub. The last image you see is of a nuke, ready for launch...
The whole concept of Rapture. It is a cesspool of moral decay, festering at the bottom of the ocean where nobody will ever find it. Scientific breakthroughs are immediately put to use in the most decadent manners possible, people abuse drugs to gain better prowess in the rapidly escalating civil wars, and a single man tries to keep his insane form of hypocritical "order", no matter the cost. And the worst part? It's all motivated by want. Ryan wanted a better place, so he built it. His idea of "better" happened to involve all the lovely things Rapture is known for pre-social collapse. So, theoretically, if someone wanted to live under the sea enough and happened to be absolutely insane, all of the horror to be found in the depths could actually happen. Hell, without Plasmids and ADAM, not much would be changed.
From Ryan's introductory speech: "A city where the artist would not fear the censor, where the scientist would not be bound by petty morality, where the great would not be constrained by the small!" Definitely sounds like an inviting place if you're a selfish bastard who is totally devoid of any sort of morals, and made even worse by the use of a Psycho Serum substance.
It was revealed that not all Little Sisters are orphans. This means that some of those girls who went on to live a life on the surface left their Splicer parents to their fate under the sea.
Could they really be saved? Or, given how many Splicers you have to fight in this game, how many of them are still alive by the time you're done?
Hopefully, if Tenenbaum is to be believed at the end of the Minerva's Den DLC, she and Porter can find a cure for the "ADAM sickness" and cure whatever splicers you didn't kill.
The audio diary "The Saturine" tells of a group of men who donned masks made of wood and leaves (ridiculously expensive in Rapture, most likely) and performed arcane rituals. This, of course, is where the Houdini Splicers came from (you find the diary in Rolling Hills, near where you fight one)... but here's a question. Did they start performing their rituals, which involved drinking blood, after ADAM really started driving people mad (Langford mentions it in the diary) or before?
Dr Langford's death. You're standing right there, forced to watch as gas floods the room, the lights cut out, and then numbers start appearing on the glass.
The concept of Rapture; of only inviting the great and geniuses to live in Rapture was doomed to failure, regardless of Fontaine's interference. [McDonagh] explains this in one Audio diary, pointing out that somebody has to pick up the garbage and maintain the toilets. There's nothing for the blue-collar worker. But in the end, there are 18,000 people living there, and a whole second generation that have never seen the sun.
Honestly, every example with splicers interacting with the environment around them (the mother wishing her baby was like he used to be, 'soft and warm and alive'; the female Splicer in the funeral home weeping over a coffin...) It's an uncomfortable reminder that under the junkie desperation and utter madness, these are— or were— very real people, mothers and fathers, friends and lovers, who all got caught up in the madness. While Rapture was undoubtedly full of selfish and hedonistic people, it's hard not to feel bad as you think more and more on what they must have gone through this past year.
The establishing moment for Rapture and its inhabitants is a banner displayed in the bathosphere tower at the beginning of the game. It reads simply 'No Gods or Kings, Only Man'. But let's take a moment to remember what humans are. Oh yeah. This Is Gonna Suck.
There's a large gender imbalance among Rapture's children. Along with the Little Sisters we see, most of the characters in audio logs talk about their daughters, such as Mariska Lutz and Anya Andersdotter. It isn't until the second game that we can even confirm that there were boys in the city. Rapture is a society built on genetic engineering, with a population hooked on ADAM, and young girls were the only viable hosts for the ADAM-producing slugs. It's entirely possible that either Ryan or Fontaine secretly introduced some kind of substance into the city to ensure the vast majority of children born were girls. They were either so desperate to keep their dying dream afloat, or so willing to make a profit off the substance, that they pretty much eliminated the viability of Rapture's second generation just so they could turn them into Little Sisters. Even without a civil war, Rapture was doomed to fall at some point.
An unintentional one, but due to a glitch in the ragdoll physics, occasionally a splicer's limb will continue to move after they've been killed. Their wrist or ankle will rock back and forth and only a few whacks with the wrench can get them to stop. With the number of splicers playing dead BEFORE you run into them, can you even be sure the ones you put down are actually dead...?