Part of the identity of any video game is how it looks on screen and how the combination of its mechanics, visual, and audio creates an aesthetic of the game. This combination evokes an emotional response from the player and defines the mood of a game.
The mood is very much part of the design like any other element, as important as gameplay or story. Games such as Limbo and Journey are essentially designed around a mood, with the specific intention of evoking certain emotions in the player as a central part of the experience.
Usually, it's not the game designer's job to define the mood of a game, but as we have seen, the mood influences the design and vice versa, so it is always an ongoing conversation ...
