Familiarity over Ease-of-Use.

In this Gamasutra articel by Ian Bogost he picks a part the old saying: "[Games] should be easy to learn and hard to master", proving that this is not necessarily the case at all.

Here are a few nice quotes that could be helpful in designing Hud elements perhaps.

"Familiarity of subjects helps apologize for unfamiliarity of form."

- Most game deal with very familiar subjects like sports (or other athletic activities), races, warfare or puzzles. Even though the control scheme in a game like SKATE is totally new, a player familiar with the subject of skating will have no problem picking it up and enjoying it (something that would not necessarily be true for someone that has never been exposed to skating and skate culture).

"Mechanical simplicity is less important than conceptual familiarity."

- You can more easily pick up complex tasks (Like playing Pong for the first time) if you are familiar with the simulated activity (playing table tennis). The same thing goes for most of what the FPS experience is all about, navigating in 3d spaces and the use of firearms (although not necessarily direct experience) are concepts we are all familiar with even though the paradigms of WASD + mouse or the two analog stick-game pad used for navigating and firing are quite hard to master the first time you try.

"By culturing familiarity and constructing a habitual experience. By finding receptors for familiar mechanics and tuning them slightly differently, so as to make those receptors resonate in a new way, and then coupling those new resonances with meaningful ideas, practices, or experiences."

- This quote highlights the need to innovate with a sense of conservatism. It might be better innovate from within persistent paradigms than attempting to "brake to mold" every time you make a new game. Part of the appeal of both RPG's and FPS's are the fact that they are so familiar to the player. You can take with you many of the lessons learned through yers of gaming and directly apply them to the next FPS on the market. The "Tuning of mechanics" that Bogost talks about are thing like the destructible environments in games like Battlefield BC that makes you challenge your "old" knowledge-set and forces you to approach the game in a slightly different manner than those you played before it- thus retaining a sens of habitualness whilst still affording new and unique experiences.