A well thought out design provides a rich environment, story, characters and interface that all work together to integrate the player seamlessly into the game world. Art is the first thing you are exposed to when playing a game. Done correctly, the mix of visuals and sound work together to bring the world to life and draw the player fully into the game environment.
Programming is the glue that ties everything together.
Good programming works behind the scenes allowing the player to experience the fullness of the effects, art, sound and environment for a complete gaming experience.