Defining Game Mechanics, what makes a game fun?

As a request, I decided to jump ahead and discuss Game Mechanics.

Game Mechanics are core features that define the game. These features are what separate the game from other games. Game mechanics highly differ depending on genre of game.

Some game mechanics often cross over from-game-to-game. These mechanics are what we call Staple Mechanics. Staple Mechanics are a good thing. They allow for players to immediately get into a game with an easier learning curve.

Game Mechanics can be anything, here are a few staple game mechanics they're seen in almost all genres:

HP Bar/Ammunition
Targeting System
Minimap
Standard movement controls (Directional, Click, or WSAD)
Story guided gameplay
Interaction/Attack function
Additional Attack/Interaction function (for more strategy)
Clutch function (Something to use on rare occasions that get you out of hard situations)

These are a couple core mechanics. They're fairly universal in almost any genre from fighting games to puzzle games.

Game Mechanics come in many different ways. Mostly game mechanics are the back-work in the game that makes it a playable experience. But also, its the strings that attach the player to the game in whatever means necessary. It could be from your interface, the fluidity of the controls, the combat design or even the interactivity found within the game itself.

Developing interesting mechanics are often difficult, the mechanics should be easy to understand, but also entertaining. Without them, the game is a lifeless, entertaining experience.

So what makes a game fun? It's the game mechanics. How do you make a game mechanic fun?

First off you need to know your audience and genre. A game mechanic designed for an older playerbase may be too complex for a younger audience. Likewise, a more simple mechanic may be uninteresting for an older audience.

While the target audience increases in age, the difficulty for the game should also equally increase. This does have a fall-off point around late 20's to mid 30's. This is due to the majority of that age ranges' reasoning to play games is typically casual short-term recreation. Where as the age range for 14 to 18 is more centered around immersible, long-term recreation. Genre doesn't particularly work hand-in-hand with age range. There are certain genres that go well with others, but for example, the Puzzle game genre is pretty much justifiable for any age range.

Once your audience and genre are established, now you can really start figuring out what game mechanics should be incorporated. All genres of games have staple mechanics. Without them the game would fall apart. For example Hack-And-Slash games, an HP bar is a staple mechanics. In a shooter game, Ammunition is a staple mechanic. In a platforming game, jump mechanics are a staple mechanic.

Once the initial staple mechanics are put in place, then you can start defining what makes the game unique to every other game in the genre.

In Super Mario 64, changing your hats to allow access to new areas was one of many mechanics set in place.
For Halo, to allow a more fast-paced, and freely short-term recklessness factor, the energy shield mechanic was implemented.
In Max Pane, bullet time was created to give the player a moment to assess the situation, and strategically find a way to get through it.
For Final Fantasy 7, the Materia system was created to give more in-depth character customization than just standard equipment upgrades.

What makes all these mechanics fun are the connection they have with the genre, none of them are necessary, but the make the game stand out and enhance the rewarding experience of the game, making it more meaningful to the player.

Because of the vast possibilities that game mechanics can have, going into each section of game mechanics would take an eternity. However it is important to know that the game mechanic should in some way, psychologically affect the player, allowing the player to have a more engaging experience, understand an objective more clearly, give the player additional options, change the difficulty of the game, or improve upon duration of gameplay. There are many other ways game mechanics can be added, but these are very important factors to this section of the game design process.