Introduction

Back in the early 2000s, there was a paper published by Robin Hunicke, Marc LeBlanc, and Robert Zubek, introducing the concept of  'Mechanics, Dynamics, Aesthetics'.  It was one of the earliest attempts to formalize game design.  It's fundamental to how we look at game genres, and it teaches some very helpful lessons to new game designers.

This article will help you to begin looking at games differently; not by the rules they use or the things you do while playing them, but by the underlying reasons one might find the game interesting or appealing.

For designers, deciding those reasons early when designing your game will help to focus you on the things that you find truly important for your game, which will result in an altogether more organized and powerful game experience.

For game players, knowledge about these reasons will help to tighten your grip on what you truly enjoy in your games, which can help you better decide which games to buy in the future.

Note:  This article draws from, and at times may quote or paraphrase, the information presented in this video:
Extra Credits - Aesthetics of Play (on YouTube).

Mechanics, Dynamics, Aesthetics

The Mechanics, Dynamics, Aesthetics (MDA) approach provides a new way of looking at games that categorizes their individual aspects.
As well as this, it points out some glaring flaws in the way we categorize our games by genre - but before I get to that, here's what the Mechanics, Dynamics, and Aesthetics actually mean:

Mechanics - rules and mathematics behind the game, like the physics, damage and health systems, etc.
Dynamics - the experience and actions the player takes when playing the game, like running around, doing parkour, battling monsters, controlling an army, etc.
Aesthetics - underlying reasons we go to the game; what it offers that we find interesting and fun; e.g. the fantasy of being a monster-slayer/marine/soldier, the challenge of beating the game, etc.  Games often only focus on 2-4 aesthetics, though elements of other aesthetics might be included here and there.

The mechanics come together to make the game's dynamics, which form the game's aesthetics of play.
Game designers and players approach this from the opposite ends: players most directly experience the aesthetics, and designers start with the mechanics and build their way up.

Unfortunately, this sometimes leaves designers so focused on mechanics that they're not actually thinking about the aesthetics of play they're trying to deliver, which can result in hackneyed games that don't seem to have any focus.
Or worse, they mistakenly think that specific mechanics will always deliver specific aesthetics.

Genres

Now, back to genres.  Let's look at the names of movie genres and game genres.
Movies have comedy, drama, action/adventure, and documentary (among others).
Games have first person shooter, real-time strategy, roleplaying game.

Movies label their genres by the underlying reason you go to the movie: what you're looking to experience while watching the film.
Games label their genres by silly things like first-person shooter: you view the game through a first-person camera and you...shoot things.  Or real-time strategy: it's not turn-based and there's strategy involved in some way.  Role-playing game: you play a role.
These labels are general and indescriptive, as well as shallow: they don't portray much of what's truly important about the game: the aesthetics of play, not the dynamics.

For example, let's take Portal and Fallout 3.  Both of these games have a first person camera and involve shooting, but they just don't fit the 'first-person shooter' category.  They are fundamentally different from other first-person shooter games, like Call of Duty and Team Fortress 2, because they deliver on different aesthetics of play.  You go to Portal for a much different game experience than you would go to Call of Duty for, because, though both games are first-person and involve shooting, they differ in aesthetics of play.

Fallout 3 and Portal have an emphasis on narrative, and Portal is more of a puzzle game than a shooter.  Call of Duty games emphasis competition and online play, and focus heavily on shooting and killing.

Aesthetics of Play

Before we get into the specific aesthetics, note that many games contain elements of many different aesthetics, but they usually only focus on 2-4 of them.  It's more important to get to these 'core' aesthetics that more strongly define the game.  For example, early Mario games included narrative, but the narrative isn't really a reason people would play the game, because it didn't focus strongly on narrative; it was more of a challenge game.

OK, here are the aesthetics:

• Sense Pleasure:  Enjoyable to the senses; good graphics/sound and music/stimulation of feelings.  Video games usually don't stimulate physical feelings very much, though some Kinect or Wii games, like a dancing game or a Rock Band game, may deliver here.
• Fantasy:  Playing as something you aren't able to be in real life; a soldier in war, a hunter, etc.  Generally, RPGs deliver this kind of experience: you become an adventurer on a journey.
• Narrative:  Intriguing and well-designed game narrative.
• Challenge:  Overcoming arbitrary obstacles.  Platformer-type games often use this aesthetic (this was a core aesthetic of early Mario games).  However, challenge is not difficulty; making something really hard isn't essentially making it a good challenge.  Difficulty is certainly useful when defining challenge, but don't take it too far.  Sometimes, challenge can include just trying to beat your high score by playing better.
• Fellowship:  Cooperation and working as a team; MOBA-type games often feature a lot of fellowship (required to win, that is).
• Competition:  The urge to express your superiority and dominance over your peers by crushing them in competition.  Usually, this is through multiplayer online games like Call of Duty, Halo, Warcraft, and so on, but minor elements of competition can be found in simple Flash-based games with online high-scores.
• Discovery/Exploration:  Finding new things.  This isn't just related to exploring the terrain of your world: it can include many things, including unlocking hidden spells, crafting new items, and so on.  Minecraft uses discovery in a few ways, one being exploring the randomly-generated terrain, and two being crafting new items.  Games with a lot of choice in them often have a focus on discovery, because it makes you want to find out what happens based on what you choose to do; this kind of focus on discovery often gives a good boost in replayability.
• Expression:  People like expressing themselves, whether it be through their equipment choices or their play-style.  Games that cater to this aesthetic will often provide lots of customization and try to push the capability of being unique and standing out amongst other players; lots of online RPGs cater (sometimes only minorly) to expression by introducing lots of different pieces of armor and weapons, classes, skills, etc. that players can customize their characters with.
• Abnegation:  This is kind of like "zoning out" by playing a game.  Sometimes, you don't want to play a game that makes you think very much or try very hard; you just want to turn yourself off for a while.Grinding in games often offers a form of abnegation (whether intentional or not) because you don't really do that much while grinding, other than the same (often simple) tasks over and over again.  Sometimes, these games don't even have ultimate goals, like unlimited mode in Bejeweled.

New game designers often think that making a good game is as simple as combining all of the coolest features that they've enjoyed most from other games; MDA teaches us that this isn't always the case, because it may very well result in a hackneyed game design that just seems all over the place.

If you understand the aesthetics you're trying to deliver early on into your game design, then you can build your mechanics and dynamics to highlight those aesthetics.

The aesthetics are the thing you should truly be focusing on, not dynamics or mechanics, because the aesthetics are what the player directly experiences.

Conclusion

The MDA (Mechanics, Dynamics, Aesthetics) framework helps to teach game designers that specific dynamics and mechanics in a game do not always translate to specific aesthetics.

Focusing on the aesthetics of play you want to deliver and trying to make sure your mechanics and dynamics highlight the aesthetics will help you create sophisticated, focused game designs.

As well as this, MDA can help game consumers better decide which games they most enjoy by categorizing games by their core aesthetics of play rather than genres.

Further Reading

If you're looking to delve deeper into the subject of Mechanics, Dynamics, Aesthetics, read the full paper here.
Also, you may be interested in checking out the video that I mentioned at the start of the article, which is what provided me with most of this information (and the paper provided the video with the information).

Article Update Log

22 March 2013: Added link to video in Further Reading; added a paragraph to the Conclusion; added more information to the Introduction; added more information after the aesthetics list.
21 March 2013: Initial release