User interface studies

One of the jobs I see more often being advertised is for a UI (User Interface) designer. So far I thought that the idea of creating a UI was more related to a graphic designer and that it didn't have much impact on the game overall.

Astronautsally's character has her health and mana bar in her stocking.

After trying to get my head around some basics I came across several blogs and writings explaining how it has been implemented, how delicate it is and versatile this can become. Understanding this, I understood the massive importance this has in creating a game as it is the direct interaction between the game narrative and the user itself.
Gamasutra has two really good articles about it explaining the types and funtions of the UI interface:
Game UI Discoveries: What players want and The User Interface Continuum: A study of player preference.

We see user interfaces everywhere; we interact daily with them that we probably take them for granted. In this case not only for videogames but it is clear that it can be implemented in many other aspects like film and animation with the mere purpose of defining the aesthetic style, just like they did in Evangelion 3.0.

The understanding of how the UI works it's the easy part I would say; it's relatively easy to adapt the fonts and the look to something that fits the style of interaction. The difficult part comes when it come to the user's respond; how can you make sure that the user will find the interface intuitive, attractive and efficient? -- by understanding your target audience.
This could be a whole blog itself and it's probably too complicated, but I found this youtube video that might help to synthesize the whole topic: