Diegetic user interface elements are closely related to the narrative or story the player is experiencing within the game. Diegetic elements exist within the game world so the player does have the ability to interact with them through visual, audible or by means of touch. Well-constructed diegetic user interface elements can enhance the narrative experience of the player. But if used in the wrong way can prevent a player from enjoying parts of the game.
Far Cry 2 largely used diegetic elements in their game. A lot of the information the player would usually see on a HUD was instead implanted into in-game gadgets like a map, compass, watch, or GPS. This method adds a sense of reality to the story and game world. In some cases though, Far Cry 2 uses a traditional HUD to complement its diegetic elements, like showing waypoint arrows on the map. Some would argue that without going all the way in terms of diegetic interface, that this mix of the two is a failure. But it can also be argued that this is as far as Crytek’s diegetic interface could go before losing the patience of the player as seen in many other games.
One example of this would be in the game Metro 2033. This game is about a community living in the underground metro station after the radiation from a nuclear bomb had destroyed their town above. They have to fight against the creatures above that were infected by this radiation. Because this narrative involves a man struggling to succeed these obstacles, 4A Games’ thought it appropriate to make it a nearly 100% diegetic experience. There is no HUD for example, guns have to be manually reloaded, and gas masks drown out environmental noise vital to hearing enemies approach. This was a very bold step for them to go this route and overall went well for them review-wise. But alas there were many players complaining of the time lost because of the diegetic elements. Some players would rather focus on the core mechanic rather than spend more than 10 seconds loading a gun.