One of the things that players of games notice intuitively is their user interfaces. Small things make a game’s interface fluid or clunky, and ugly or beautiful. A designer who isn’t careful can introduce unnecessary elements or hide crucial information and functionality, crippling their game while working on a part of it that is often underrated. Furthermore, interfaces set the mood of the game before any of the other art and mechanics come to the forefront.
A good interface sets the mood for a game. Sometimes this occurs through functionality; Arma’s cut and dry interfaces further emphasize the no-nonsense nature of the series. Other times this is done through color, design, and placement decisions intended to create a specific response; a main menu with futuristic, sleek interface elements comes across very differently than one with a full three-dimensional interface that resembles medieval signs hanging from a beam. Shadowrun Returns, for instance, immediately looks like a cyberpunk game, while Baldur’s Gate’s main menu is obviously fantasy-inspired.
Placement of user interface elements is obviously important. Dark Souls would seem a lot less threatening if it had an user interface that focused more on telling the player their current statistics and if it flashed warnings up on the screen; its small and streamlined interface leaves more room for the player to see their environment, but also means that checking vital statistics requires an additional action. This gives it a much more difficult feeling. Killing Floor uses the lack of a crosshair to increase the difficulty of its action-horror gameplay, with players forced to guess where their shots will land or actually slow down to aim.
Furthermore, the style of an interface is important. A transparent, frequently hidden interface is much more immersive, and if combined with sleek bars or meters reflects something like Metal Gear Solid or the Arma 3’s sleek minimalistic style. On the other hand, an interface can also be intentionally flashy and artistic; many of the Final Fantasy games stand out even among the JRPG genre for having a very fancy user interface, with lots of information on the screen but presented in a very simple manner, looking very much like a traditional tabletop game character sheet but with all the flair that a digital environment allows. The health bars of a fighting game not only indicate which side of the screen a player is (or starts) on, but are built to flow naturally into the screen experience, even something as simple as the health bars of the original Street Fighter are built to serve as a sort of progress meter, with a timer surrounded by the current status of the combatants.
As a general rule, UI elements that are further out from the edges of the screen feel more important; in this way the lowered health-bars of the early Street Fighters (presented below the scores of the players) resemble the selective fire indicators of Arma 3; rather than sticking on the corners of peripheral vision, they are presented at a very quick glance. Note, however, that while Street Fighter has its health-bars front and center, Arma 3 pushes the ammo counter and selective fire to a corner, meaning that updates to the information displayed on the interface are less likely to become immediately apparent to the players and encouraging further immersion. On the other hand, you have a game like Warframe, whose user interface elements are much smaller than those of Arma. When playing Warframe, the act of checking health and energy levels is not a reflexive action, and as such players have to breach their concentration to check their current health, ammunition, or power availability.
In order to fully manipulate mood with user interface elements, it’s important to consider the impact of the art. Metal Gear Rising: Revengeance or Deus Ex: Human Revolution do a very good job at creating futuristic vibes for their displays; sharp edges on interesting shapes provide both utilitarian and sleek designs. Human Revolution incorporates a hotbar and a grid-based inventory as a shout-out to its RPG elements, while Revengeance incorporates a combo counter in the Metal Gear styled military LCD readouts. Compare this to something like Path of Exile, which is immediately obvious to a common observer as a Diablo-styled RPG through the use of the iconic health and mana globes, its dark metallic Gothic-styled elements and the presence of hot bar elements that would be stereotypically associated with such a game.
When considering how to really bring the feel of your game together, consider working with the user interface; it can do a lot for the mood, and there’s a reason you almost never see a triple-A or even well-polished indie game ship with bland and boring, purely utilitarian, user interfaces.