Aesthetics are one of the four columns of game development. No one likes to play an ugly game, no matter how good the mechanics, the story or the gameplay is.
An ugly game goes not refer to low technology or unrealistic graphics. A game can be beautiful with the lowest technology possible or the most unrealistic of design.
Beauty, as defined, is to be visually pleasing. Now what constitutes that in games?
Obviously, massive amounts of polygons, amazing textures and realistic design can attract many eyes to your game, but is ultimately just eye candy that’ll get old without the real element of beauty: Atmosphere.
Every game has a theme, a setting. Every frame is a moment of art, every frame is a painting. Every frame is a chance to let the player feast on a sea of emotions. True beauty is the art of being able to convey you desired emotion through your visuals, and to convey the right emotions at the right time to reinforce an enjoyable setting.
The art of placing every prop at the right place, every sound, every footstep, every source of light, to reveal the artistic core of the game.
To create an atmosphere, an environment, that drags the player inside the screen whether they like it or not. To draw their minds away from the reality into the world created, to every bit of color and shape that creates the perfect atmosphere in a game.
Beauty is not only art either. You must engage as many sensory abilities of the player as you can. You can see the technologies arising that allow the player to hear, see, feel and interact with the moment. Every one of these elements is crucial in creating emotions and making a beautiful game.
Therefore beauty goes not depend solely on the elements of technology and realism, but in creating the right atmosphere to convey the feelings that you need in the setting. Your art style can be in pixels and the game can be beautiful. Your models can be less than 200 polygons each and you can still have a beautiful game. You can have no textures and plain colors and still have a beautiful game. The only thing you need to do is to artistically engross the player’s feeling into the world you’re trying to show.