Atmosphere (In Adventure Games)

Creating (a believable) atmosphere in adventure games can be a very hard thing to do sometimes. But there are some key things that can boost the atmopshere in your game, and once you know them, they are easy to apply.

Each item is labeled with a number and a plus. E.g. "+5"
+1 (min) Means that this will help the game a little.
+5 (max) means that this will improve the game ALOT.

1: Animated Backgrounds +2
Lots of places in real life are not still life. Trees wave in the wind, lights flicker on and off, doors open and close, and some things are shiny. Having a blank slate of a background can be okay in most places, but making it animated can make it awesome.
E.g. trees blowing, grass moving, water rushing, dirt blowing, lights flickering, fans moving, etc.
2: Animated Objects +2
Self-Explanatory. Interacting with objects in the world, and then having then animate, makes the world seem so much more alive.
E.g. Doors opening/closing, cabinets opening/closing, turning on machines, turning on lights, using computers, using tvs, picking up phones, etc.
3: Animated Characters
3-1: Actions +3
All player actions should be animated. The animations don't have to be a smooth 10 frame animation. They can be simple, but having 1 frame is 10x better than nothing, and have 2 frames is twice as good as one frame. And having 3 frames will make it seem very smooth and believable.
E.g. The character animates for: picking up items, reaching up high, reaching down low, falling down, sitting, opening objects, using objects, etc.
3-2: Speaking +4
People don't just open and close their mouths while speaking to each other; they make gestures. People cross their arms, kick the ground, wave their hands, shrug their shoulders, or put their hands in their pockets.
3-3: Idle +2
People do not just stand idlely on the side of a path waiting for you to trade an object with them. As funny as it may sound, PEOPLE DO THINGS. Nobody stands around doing nothing unless they have a specific reason. But if you can think up a reason for why someone is standing there doing nothing, then that's good, and you're all set.
But you have to make the character animated, no matter where he's standing. NOBODY just stands or sits somewhere and stares straight all day, unless they have a serious problem. People turn their heads, change their postures, move their legs, and other stuff.
4: Sound Ambience +3
Unless the location the player is in literally has dead silence, you need to have some kind of background noise. For city scenes you can have crowd noises. For outdoor scenes you could have the wind blowing or animal noises. For ocean scenes you can have the waves hitting the rocks or sliding up onshore. For indoor scenes you could have the sound of machinery humming or something.
5: Sound Actions +2
Every individual action the player can preform should have some kind of sound. The sound can be loud or subtle, but opening doors, picking up objects, walking around, using computers, etc. should all produce a sound effect.
6: Music +5
In my experience, the difference between a good game, and the difference between an unforgettable game is most often times the music. Great music can stick with the player forever, and improve the atmosphere ALOT. Don't underestimate the use of music in a game.
7: Writing +4
The things people say, or the things people do can be the base for the whole atmosphere. If a serious game suddenly breaks the 4th wall, the atmosphere is destroyed. If characters do things or say things that are totally ridiculous (and usually the author doesn't know it), then the atmosphere can be destroyed.
The level of seriousness/funniness should be maintained in a game, and kept consistent, otherwise the player will lose his sense of disbelief.

Atmosphere in games comes down to 3 things:
GRAPHICS: Animations, characters, objects, backgrounds
AUDIO: Sound effects, ambience, music
WRITING: Story, dialogue, etc.
Either of the items/sub-items can improve the atmosphere in their own way, or on the contrary, destroy it.