http://www.gamasutra.com/view/feature/1524/the_chemistry_of_game_design.php?page=2Play is instinctual. In low stimulation environments where we are not actively pursuing activities related to food and shelter, people will begin playing by default. Strong feedback mechanisms in the form boredom or frustration prod us into action. Given a spare moment, we throw ourselves into playing with blocks or dolls as children and more intricate hobbies as adults. It is a sign of our need for meaningful stimulation that solitary confinement remains a vicious punishment for the most hardened criminals.1
The flip side is that we are rewarded for learning. The sensation that gamers term ‘fun’ is derived from the act of mastering knowledge, skills and tools. When you learn something new, when you understand it so fully you can use that knowledge to manipulate your environment for the better, you experience joy.
There is a reasonable amount of neuroscience available to support this claim. Edward A Vessel, a cognitive neuroscientist at the NYU Center for Neural Science writes:
“These “aha” moments, when a concept or message is fully interpreted and understood, lead to a flood of chemicals in the brain and body that we experience as pleasurable. It feels good to “get” it. The deeper the concept is, the better it feels when we are finally able to wrap our head around it.”
Upon the click of comprehension, a natural opiate called endomorphin, a messaging chemical in the brain similar in structure to morphine, is released. As humans, we are wired to crave new information constantly. In some sense, what you and I term curiosity can be interpreted as our brain looking for its next fix of deliciously fascinating information.
Ever seen one of those big colourful things from the 80s where they say "learning is fun"? You know, these:
They weren't kidding. Learning is fun. Learning is like taking goddamn heroin. Without any of the downsides.
Now, there's no question that people mean different things when they call games "fun" (I'm sure some of you have read Mark Rosewater's Timmy/Johnny/Spike), but I'd estimate that a good 70% of people, when they refer to "fun", they're referencing the psychological state of play. And since the psychological state of play is the primary method of human learning (and mammal learning, for that matter), we can actually say that fun is literally learning.
And once we realize this, we get a large knowledgebase at our feet--namely, all the academic research done on Education. We know, for instance...
People are highly resistant to un-learning things they already know (which is why you get nerd rage when you can't invert analog aiming in console games).
Learning works like a tree structure, with more advanced concepts being built on less advanced concepts. You need to be able to jump before you can jump on a platform. This also has implications for re-learning--if you're going to make people re-learn something, make them re-learn it at the top of a tree. When you do something like invert people's aim controls, you not only disrupt their learned aiming skills at the base of the tree, but all the skills further up that tree branch too, like "aiming while moving, jumping, crouching, and shooting".
Synthesis is challenging. People tend to compartmentalize their learning, like "I freeze blocks to get past those pits" and "I dig to get around those obstacles". Thinking like this makes it very easy to miss moments when "I'd normally dig to get past this obstacle, but freezing is better." Or, moments like "If I freeze over here, it will allow me to dig when I otherwise wouldn't be able to."
And so on (I don't have a degree in Education; others can probably fill you in more than I can).
So...knowing that we're trying to design something that maximizes people's play-state and learning, even if the learning is not directly applicable to anything in the real world, how do we do this?
One way is to make a system with a fixed number of rules but nearly unlimited depth, so that there's always something new to learn. Chess or Go, for instance. (I believe there are more books written about Go strategy than any other game in the world--clearly a lot to learn--and the game has, what, four rules?) This appeals a lot to some people when done right, but has some downsides. First, it's really hard to make these games. Second, it's going to miss some audiences--the player needs a good deal of self-motivation to either network with people smarter than herself and learn their strategies, or desire to experiment and compare the effectiveness of various strategies knowing full well that most experiments will be failures from which she will learn little.
The second way is to just provide the player with lots of small easily-learnable chunks. This will feed new players with a constant, unbroken stream of learning, but may lack replay value. For an example, let's look at Super Mario Galaxy 2.
Star 1: reintroduces the basic jumping mechanics from 3D Marios. Has some platforms that rise up and disappear (which may not have been in SMG1). Has a boss that's...slightly different from past SMG bosses (although trivial if you're used to SMG bosses).
Saddle Up with Yoshi: makes you learn riding Yoshi, swinging from flowers as Yoshi, eating enemies as Yoshi, dragging large drawers with Yoshi's tongue, fluttering with Yoshi
Storming the Sky Fleet: Introduces Circular/Curl gravity (gravity that works like magnetism, where "down" takes you around the center of gravity). Introduces phantom Marios that chase and try to kill you. Also a bunch of things that haven't shown up yet like keys, various new enemies, colour-changing panels that you need to change from blue to yellow.
Spiny Control: introduces spitting things with Yoshi. Makes you aim what you spit. Makes you jump and spit. Oh, and makes you fight a boss where you have to jump and spit while avoiding increasingly complex patterns.
Spin Dig 1: Introduces Drill Mario. Makes you use Drill Mario to drill to specific points on the other side of a planetoid (in increasingly complex ways, like drill sequences). And...gives you a boss with boss patterns to learn.
Spin Dig 2: Introduces using Drill Mario in 2D situations, including stuff like bouncing off of 45 degree slopes. Introduces Drill Timing, where you need to time your drill so that you don't hit electrical enemies on the other side. Has a bit of a memory game going, where you need to remember the layout inside of the dirt to figure out where to drill. Brings back the "collect 5 silver stars" mechanic. Brings back the "kill a pirhana plant, get a massive vine" mechanic.
Flip Swap Galaxy: Introduces the "shake = platform change" mechanic, and makes you learn to deal with how that interacts with "shake = double jump". Brings back some more enemies/obstacles.
Fluff Bluff Galaxy: introduces Cloud Mario. Teaches you that Cloud Mario should fear water. Brings back some enemies.
Fluff Bluff Galaxy 2: Intorduces this crazy jumping minigame where you're trying to score points by killing lots of enemies quickly and getting combos. When to jump on enemies heads and when to run collect coins before they disappear. Completely new skills to learn.
Fluff Bluff Secret: Brings back coin-hungry Lumas. Makes you search for secrets. Makes you do "grab this coin formation before it disappears". Has a basically 2D Cloud Mario sequence.
Rightside Down Galaxy: throws you into a 2D Sequence where you can alter the direction of gravity by flipping switches. Makes you do problem solving with this mechanic. Introduces new enemies. Brings back the fire flower. Brings back burning through obstacles with the fire flower. Requires wall jumping (or at least a backflip). Brings back overhead 2D-Zelda style sequences. Introduces sideways gravity right at the end.
Rightside Down Secret Star: Brings back "burn some boxes in time X".
Bowser Jr's Flotilla: New boss with new patterns to learn. Brings back a bunch of old enemies like rotating firewheels.
Interspersed with all this, your spaceship is getting updated and you can learn where everything is, slowly growing your knowledge. You get to learn a new world map system. New and old characters get introduced. Your brain is subconsciously learning new music.
Basically, SMG2 here gives the player new stuff to learn at every star (even the players who've played SMG1). We can say, with quite a bit of quantifiable measurements to back us up, that the first world of Super Mario Galaxy 2 is "very fun". (Or, a bit more rigorously, it's very good at creating the play psychological state).
I'm sure there's some skeptics who are saying "so all I have to do is throw 20 different minigames at people?", and no: that would fail badly as game design. People are attracted to learning things that they feel will be relevant. In Galaxy 2, the core jumping mechanics, the core navigation mechanics--a.k.a. the core skeleton of player knowledge--remains intact between all of these levels (no water level!!!!) Even a lot of the new skills end up similar in player execution--Cloud Mario tends to jump and spin. Shooting with Yoshi is a jump and spin. The Flip Swap Galaxy is about jumping and spinning. And with all these power-ups and mechanics there's the promise of "there will be more levels like this later, so you should really learn this mechanic". All of this comes together to make the brain think "This is relevant information that I want to learn because it will help me later"--a necessary state-of-mind for learning.
Let me end by saying that you don't have to focus on the psychological state of play. It's hard to imagine a game that would never once put the player into this psychological state, but there are definitely games where the primary focus is on other psychological states, like relaxation or competition or fear. Certainly not every game has to be Galaxy 2, where the game completely bends over backwards and twists itself in half to give you steady shots of fun at least once per minute. But that is also a viable game design direction, and something that's handy to have in your game design toolbox.