These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Breather Level: After the heart-stopping panic of the water demon in the cellar Daniel arrives at a peaceful (if slightly bizarre) Back Hall. Then it turns From Bad to Worse. So much worse.
It's worth noting that this was an Invoked Trope by the Dev team, as the dev diary in the area notes that they wanted to give the players a break to "reset" before ramping up the scares again.
Comedic Sociopathy: The game is horrifying to play, especially alone at night, but watching other people play it while freaking out is inherently hilarious. You will probably be whimpering/screaming profanity during gameplay, but that doesn't stop it from being terribly amusing. Playing it with observers on On Live is a good example of this.
This one might be the best known, and is notable for being the source of the minor fandom meme "Oh shit, I have a bag of Milky Ways."
Companion Cube: Not so much on Daniel (the player character)'s part, but many players will find and cling to some item in the environment as a security blanket — for example, PewDiePie often picks up (and talks to) random objects, naming and giving them voices, as a self-comfort measure.
The lantern may be this to some players considering it is a source of light that is always with you through most of the game and helps maintain your sanity.
Also main Cistern area and where you meet Agrippa in the Nave, which works as a breather room
Evil Is Sexy: Alexander — or at least his voice. Daniel too, for many fangirls, though he does seek redemption.
Foe Yay Shipping: Alexander/Daniel is a surprisingly common pairing, mostly because Alexander has so many shades of Magnificent Bastard to him it's not completely out of the question, and players inclined that way find both their VAs have sexy voices.
Hype Backlash: It's still a good game, but new players have started to see the flaws in the horror aspect. Depending on who you ask, the Nothing Is Scarier parts can get boring after a while, the monsters look more silly than scary, their AI is pretty poor, and the fact that you can easily avoid them can ruin the sense of danger, making them more of a nuisance than a threat. The game also still deploys some cliches of the horror game formula such as a monster appearing whenever an important item is picked up.
It Was His Sled: The game was designed to keep the monsters out of sight so their appearance would be a mystery to players. But the monster designs have become so well-known that the Grunt-type enemy is practically a mascot for the game!
Memetic Mutation: Milky Way candies, thanks to a popular video of a guy playing it while on Skype with friends, in which one mentions having a bag of fun size-versions of the candy while the Amnesia player is freaking out.
The same video introduced "That is not... traditional fire!", which briefly became a Fun T-Shirt!
Narm: In the first area of the game you can hear a strange sound coming from some sort of animal outside. While not the scariest thing by far, it's been known to spook some players. Unless those players are from Canada or the UK, who will probably recognize it as the call of the majestic aquatic bird known as the Loon or Diver.
But listen to the bird on YouTube... it's a haunting sound. "It stays with you for the rest of your life," indeed.
At some points in the game you can hear a strange crunching sound. It might be intended to be the cockroaches, but it sounds more like someone is eating potato chips somewhere off-screen.
Most Wonderful Sound: That deep breath you hear as the screen flashes blue, signifying that you've solved another puzzle and replenished some sanity to boot.
A Let's Player named Cry has taken to playing a number of the downloadable custom stories created by Amnesia players. Luckily for us all, he seems to have a great knack for turning a terrifying encounter with a bloodthirsty monster into utter hilarity. This probably has a lot to do with his somewhat eccentric habit of holding lengthy conversations with inanimate objects in the game, such as a wardrobe, a statue of Jesus and "Mr. Cog".
Rutskarn: Just bunny-jumping down a corridor, haunted mansion, real spooky: "doot doot doot doo". Shamus: The monsters are all like, "I'm not going after him; that's a Counter-Strike player, screw that guy."
PewDiePie's playthroughs are brilliant in their own right, but his reaction of pure joy whenever he discovers Stephano (a little bronze or gold figurine found in many rooms on the map), Piggeh, Mister Chair, and Skully, his distrust of barrels and suits of armour and his yelling at "Teleporting Naked Guys" makes the game a lot less scary to watch.
Lanipator is just so calm when he played. He makes the game look like an average scary game. He makes great jokes. He makes the scary moments funny by mocking Daniel's weakness or demonstrating how stupid the monsters are. He doesn't usually scream when something scary jumps out. He just uses logic and hides or runs away all the while staying focus on how he can survive. It's just unbelievable how calm he is. He even lampshades it. It's almost like it's just another day at work for him — perhaps because it is?
This video uses a mod that replaces the voices of the monsters with the yells of the guy from the yelling at cats video. It takes the eeriness out of the game, and makes you laugh your ass off.
Agrippa's introduction can come with a bit of a Jump Scare when you see his Facial Horror. However, do what he asks and pull the lever, and you'll see he's actually a nice guy (though his sense of humour is a little odd).
The flashback scene where Daniel ritually kills a prisoner would be otherwise horrifying, but the way he mockingly recites their pleas for mercy comes across as hilarious.
Paranoia Fuel: Directly related to Nothing Is Scarier. Monsters really don't appear that often, and none of them actually attack you until a good 1/3 of the way into the game... but you'll be surprised at how often you wind up hiding in a cabinet or corner because you think you heard a monster.
In addition to that, there is the fact that if you are killed and have to reload, the game will occasionally make the monster that killed you not spawn at all. Maybe. Occasionally. It doesn't happen often enough to rely on, but it does happen often enough that you will spend an extra 5-15 minutes sneaking and running frantically from a monster in an area the game has decided to clear, just for you. And the game gives absolutely no indication of when it decides to do this. And you usually don't find out whether the game is giving you a present or a box of spiders until you round a corner and run into another monster that the game has spawned for kicks and giggles.
This game will make you hydrophobic.
Not to mention that the castle is filled with enormous (hand-sized) hissing cockroaches. They don't do anything and they can't hurt you, but when you get near one, it hisses at you. This can be unsettling.
Player Punch: While you might suspect what Daniel had done prior to his amnesiac state, the full grasp of it won't hit you until you reach the Torture Cellar. These are scattered about to lesser degrees throughout the Torture Cellar, as well — you'll feel like you've bruised your ribs by the end of it.
Sequel Displacement : Arguably this towards the Penumbra series, probably because it's a stand-alone and had more adamant marketing (mainly by word of mouth on the internet via Frictional's long-time fans).
That One Level: The Choir. It's huge. It's open. It's easy to get lost in. And there are Brutes everywhere. There are no dark places to hide in either; when one appears, all you can do is duck behind one of the room's many pillars and hope he doesn't come too close. The three rooms you're supposed to go into will drain your sanity just by being inside them, and they're loaded with Schmuck Bait that will reduce you to a gibbering wreck quickly.
That One Boss: Malo from Justine. While you only have to avoid the other two suitors, Malo you have to outrun through several puzzles that the physics engine can make frustrating. Worst of all, Malo is at the end, and if he kills the Player Character you have to go all the way back to the beginning. Which is made worse by the Player Character being a One-Hit-Point Wonder.
Uncanny Valley: Deliberately invoked with the Grunt; in what looks like a pale, drooping corpse, there's a jaw that looks like it was designed by Salvador Dali.
The Woobie: Yes, even in this horror-filled game there is still a woobie — Daniel. Listen to some of his dialogues (especially the one where he is in the storage "but why is it so dark?" and the one about the morgue).
The little girl as well: "Please let me go! I won't tell anyone, I swear! I just wanna go home!"
The second Suitor from Justine. Justine is a bitch.
Just listen to Alois's dialogue and try not to feel sorry for the poor lad. Even after everything Justine did to him, he still adores her and just wants to be with her. Albeit via murder.
Alois: Is that you, my love? You came for me!... Where did you go?! Come back! Please, come back!