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.
A-Team Firing: A common complaint against the game is the lack of feedback on whether shots hit or miss. Depending on skill level, this trope may or may not be in effect because of this. Might be somewhat justified considering the quality of the firearms you find.
It's basically S.T.A.L.K.E.R., except more linear. Bonus points for 4A Games actually being founded by a couple of people who were involved with Stalker's development, specifically the underground lab levels. Both are also based on sci-fi novels by Russian authors.
Goddamn Bats: Appropriately enough, Demons. Only encountered above ground, spend most of their time flying around above you, annoying as hell when they decide to dive-bomb you.
And the Lurkers. They swarm, take up ammo, and can dive into their instant-kill rat-holes at a moments notice. They also scream loudly and unsettlingly, either screeching like bats, or roaring like lions, neither of which are pleasant at all.
Nightmare Retardant: You quickly learn that nosalises aren't big enough to fit in the narrow pipes the game likes to make you crawl through, and lurkers won't follow you in (for no particular reason), so these sections lose a lot of their tension. This makes one Jump Scare in the Lenin Library very effective, when a Libraran's arm reaches for you out of a side-vent.
Bourbon: Some call them demons, but I call them bitches.
It is actually a Narm Charm for a native Russian language speaker, at least in the respective dub.
In Russian, Bourbon calls them Cykи (Suki), which means bitches. Cyka (Suka) is the singular.
Sometimes, you will hear enemy humans yell "DAMN!DAMN!DAMN!"
Death of Boris
Stepan: BORIS! My Friend! WHY?... The Bastards! Boris I swear on your memory - they wont rest while I'm still alive!"
And yet Stepan doesn't mind that you loot his (Boris') corpse for ammunition and morphine.
Considering how no one complained all the times you did before, it may be common practice.
The whole conflict between the Communists and the Nazis is loaded with narm. Even assuming that ideology can overcome the need for basic survival, how seriously the followers of each side take it starts bordering on absurd. It feels like both sides are World War IIWar Reenactors, only they shoot at each other with actual bullets.
Scrappy Level: The Library. There's a part where you're on a fetch quest, your enemies are Librarians, and there's no real sense of where to go because you may end up backtracking to the beginning of the section. Also, hoped you decided to stock up on ammo, because Librarians eat bullets like candy.
Just knife the damn things and run behind columns to get your health back. This even works on Ranger Hardcore.
NPCs actually instruct you to stare the Librarians in the face and back away when they approach, which means you can slip by without fighting them. Unfortunately the game can be inconsistent with this regardless of where your crosshair is facing.
It is also one of the levels where you almost perpetually need to keep your mask on, and filters are few and far between. Hope you stocked up!