Uncanny Atmosphere

An Uncanny Atmosphere is basically when the characters/audience get the feeling that something is wrong in their environment. They don't know exactly what's going on, but they do know that something is definitely wrong.

For example: character walks into an area and gets the feeling that something is wrong there. Maybe everyone is gone? Maybe the inhabitants are all brainwashed zombies? Or, everything seems fine at first. But slowly, the characters/audience start to feel an undeniable sense of wrongness in the atmosphere.

Intentional use of the principles of Uncanny Valley are often applied to setting and background characters to increase drama or hint at conspiracy. The colors are a bit off (The Matrix), the people are too nice (The Stepford Wives), everything is too clean or it's just too quiet. This may be a sign of a Crap Saccharine World.

Compare to Uncanny Village and Nothing Is Scarier.

Examples of Uncanny Atmosphere include:

Film

The Stepford Wives

Literature

H.P. Lovecraft was very fond of this trope. Whenever his settings weren't an Eldritch Location, there would still be a distinctly 'wrong' aura about them, which the narrators typically emphasized. Innsmouth was a prime example, with its dilapidated structures and fishy odor hinting at something horrible behind the scenes. Other uses include The Colour Out of Space and The Whisperer in the Darkness, just for starters.
Edgar Allan Poe: The Fall of the House of Usher
Some of Roald Dahl's stories, particularly The Landlady where early on you can tell there's something not right about that woman and her "Bed and Breakfast".

Tabletop Game

At least in recent years Wizards of the Coast has been trying to make the flavor of Magic: The Gathering sets and the game play feel like they are all saying the same thing. Except with Amonkhet. The game play was supposed to feel harsh and brutal, while most of the flavor text and images were supposed to look, at least superficially, like everything was going good. Combined, these were supposed to give a sense that something was off (which is what at least some members of the Gatewatch were feeling). The sense that the world might be much worse than it appears [1] (Note that the card in the link has the highest rarity).

Video Games

BioShock (series)
Peaceful Rest Valley from EarthBound.
Fallout 3: Vault 112.
Okage: Shadow King - The Highland Village. Everyone there talks in a distant, dreamy tone. Turns out the entire village is a feeding ground for the Vampire Evil King.
Paper Mario: The Thousand-Year Door: The Glitz Pit. About halfway through you'll be able to smell a conspiracy brewing.
In Pokemon XD Gale Of Darkness, your return to peaceful Phenac Town from the first game is deliberately designed to invoke this. New players won't see what's wrong, but people who've played Pokémon Colosseum will take notice that all of the NPCs are acting contrary to their personalities in the previous game, and the roaming Pokemon are also all wrong (for example, the jogger lapping the fountain has a Duskull following him instead of a Castform). It's unsettling, but at the same time one has to wonder if the programmers just plain Did Not Do the Research about how things were in the first game. And then you find out that Every single person in town had been kidnapped and replaced by a disguised Cipher member. Yikes. After you've solved that problem, Phenac returns to exactly how you remember it from Colosseum. Well played, Genius Sonority.
The Silent Hill series. When a character first enters the town, they notice that no one is around and even before they find their first monster, they know there's something wrong there.
Super Mario RPG: Legend of the Seven Stars - The Seaside Town. By talking to the villagers you'll eventually realize that something is wrong here. You eventually find out that Yaridovich has kidnapped all the townspeople and has disguised himself as all of them.
All of Termina from [TheLegendOfZelda:Majora'sMask\].