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If you haven't played Minecraft yet, go do so now. The $13 that you will spend will give you more hours of entertainment than any $60 AAA released this Christmas. This slow burning indie hit has been on the fringes for a few years; spreading slowly through word of mouth and YouTube videos before a few mentions on big gaming blogs like Kotaku and Penny Arcade, as well as a play-for-free session inspired by a server change, brought it to a wider audience.

Everybody that plays it talks about it, and everybody that talks about it has their own story to tell, their own achievements to boast about, their own dangers to post-humously warn about. What makes Minecraft so addictive, to the extent that it's been nicknamed Minecrack? What sort of design lessons can we learn from this still-in-alpha game?

Exploration & Growth

Minecraft is huge. An average world will apparently take you 6 real-world days to traverse. And that's just on the surface. True to its name, Minecraft has you exploring the roots of the earth in the search of minerals. When you start the game, you've nothing but your bare hands and your wits. You can dig earth and chop down trees but little else. To progress, you need to craft. So with your wood, you make planks and sticks and wooden implements, which let you mine deeper. The deeper you mine, the more minerals you can find (with the most valuable near the bedrock), the better implements you can craft.

As you mine, you can discover vast underground caves. Out of personal experience, I was mining a spiralling, vertical shaft only to break through some rock and find myself hanging a good 20 meters in the air. Below me a vast cavern stretched out beyond the meagre light of my torches. Off in the distance to the right came the glow of a river of lava, while to the left I could hear the promise of a waterfall. When I finally created a staircase to get down, it took me a good hour and a half to fully explore the cave and it's possibilities. It took me even longer to find my way back. It's so easy to get lost. The feeling of space is palpable. The urge to pick up and pack up is always a growing itch.

One of the things you quickly discover the deeper you go is that monsters spawn in the dark; monsters that can kill you before you even realise that they're there. As you mine and gather materials, you can create weapons, armour, battlements and traps to guard your back, defend your creations, or expand your base. There is no tutorial telling you to do these things, there is no "get this to go here" quests. You build armour to defend yourself against attacks. You build swords and bows to go on the offensive. As you get better minerals, you can craft better equipment. As you mine more stone, you can build higher walls, until your fortress is outlined against the very skyline.

Each time you break through the wall of an unexplored vista, the possibility of monsters invading your base, your home, becomes very real, and sets off the next steps of construction, exploration and fortification. You make your own goals, you define your own progression, but most importantly, you see yourself grow from a defenseless imposter in a harsh world to a fearless master of the environment, bending it to your will.

Fear and adrenelin

When you first play Minecraft, you're blessedly ignorant of the perils of the new world you find yourself in. As the first night falls you might admire the stark beauty that the blocky graphics afford. Then the monsters come. The first encounter with Minecraft's more evil inhabitants usually imparts an important, and probably fatal, lesson. Create shelter or die. From that moment on, you are constantly looking around you, freezing at the first hint of a sound. Minecraft is honestly one of the scariest games I've ever played.

It's not even as if the monsters have devious AI and plot together to cut off all paths of escape before falling on you. Monsters usually follow a simple straight line towards the player, often sticking behind a rock or a corner. They are however remorseless killers; two or three hits is all it takes before you find yourself respawning naked of your equipment in the middle of nowhere (you drop everything you had on your with your corpse � you can of course try and get them back...). That's not to mention the dreaded Creeper, which sneaks up behind you. Unless you're vigilant, the first indication you have of the Creeper's presence is a short hiss before it explodes, killing you instantly.

All of this combines to make you intensely wary when travelling outside your castle. You're constantly on edge, looking around every few seconds, sword at the ready. When you explore underground, light is your best friend. All the old childhood fears of monsters in the dark become real when you're faced with a pitch black tunnel deep underground. You suddenly realise just how very far the surface is. Perhaps the sword you're holding is a little on the worn side and you should go up and craft a new one. Just to be sure.

The sound is used excellently in this regard. When you're deep under the earth and the music switches to the ominous few bars that just...promise, you stop, alert. When you're exploring a new tunnel and the sound of a Skeleton drifts up, your adrenelin starts flowing and your heart starts beating faster. Exploring in Minecraft is never boring. You're never safe. When clearing ground for my castle during the day, I was ambushed by two Creepers and a Zombie. Monsters aren't meant to come out during the day! That moment of panic was something I won't forget.

With the latest Halloween update, you need more light the further down you are to stop monsters spawning in your base. A planned future update will make torches burn out after a time, which makes things even more interesting. You can now also create a portal into a hell dimension, where the sounds are quite frankly, skin-crawling. Minecraft captures the essence of fear better than other games specifically created for that purpose.

Imagination

To cast a casual glance at Minecraft, you might dismiss the blocky graphics as something that should belong in the NES age. Granted, much of the current state of Minecraft can be attributed to the fact that for all intents and purposes, it's a one man job. Random world generation and blocky graphics greatly simplify the work that needs to be done. However, this takes away from one of the greatest tools in Minecraft's belt: imagination.

Back in the eighties, the simple graphics relied on generous helpings of imagination (helped by the gorgeous packaging, an art that has sadly diminished) in order to pass off the worlds, characters and scenarios within. Nowadays, imagination doesn't have much of a place at the dinner table of gaming; leastwise the imagination of the player. There's no need to imagine what an orc looks like when an artist models and animates it for you, and this is a great loss. No amount of work on behalf of the artist will ever be able to match what a person's imagination can create. At Sid Meier's GDC keynote, he told a story of the player being able to receive a gift of dancing bears in Civilization. The bears were never drawn in the game, merely being represented by a text box. Nethertheless, it's the player's imagination that brings them to life and gives the game more colour and depth. Minecraft uses the player's imagination in three key areas: building, exploring and horror.

Sit someone down in front of Photoshop and tell them to create whatever they like and you're likely to get a blank expression, followed by the equivalent of something from the bowels of Word art. Only the genuinely artistic will produce something that other people will want to look at. However, sit them down in front of a 10x10 grid and restrict them to blocks and a few colours and then you start to see better results. In Minecraft, players place blocks to build whatever their heart tells them to. In their head enormous castles are founded, magnificent arches and bridges that stretch into the distant fog. The level of visual fidelity is such that you don't need amazing skills to realise your visions, or amazing insight to appreciate what others have built. If you played with Lego when you were young, you'll realise the similarities. Minecraft provides you the simple tools to get you to a stage where your imagination can take over.

When you explore in Minecraft, it's your imagination that transforms the blocks in front of you into the history of the world. Breaking into an underground cave is like breaking into the past. And because the world is so huge, it's your imagination that fills in all the possibilities that could be. These are the reasons why you keep digging, why you travel overland to see what you can find. What's going on in the player's head is always more colourful and interesting that what the world can provide.

One of the reasons why Minecraft is so scary? You make it that way. When night falls or the mouth of a cavern stretches out in front of you, and your cone of vision is limited by the meagure torches that you have, it's your imagination that populates the world with what could be out there. It's your imagination that keeps you behind your walls until the sun comes up. All the primal fears resurface when you're confronted with the dark. Perhaps there's nothing there, but each shuffling sound or change in the music has your imagination painting the possibilities vividly across your brain. Rather than resort to shock values (i.e. the Hollywood horror film), Minecraft is more about the psychological nature; it provides the vessel and the player fills it up.

Emergent gameplay

Because Minecraft is randomly generated, no two person's games are the same. Nothing is planned in the game. You can sit down and say that you'll mine for diamonds before being interrupted by the promise of a new cave, the unexpected mining of the wrong brick and subsequent flooding your new tunnel with water or lava, or the discovery of a spawn point of monsters which leads to new plans and designs.

While a heavily scripted and hand-held approach will provide momentary thrills, it doesn't stand up to repeated play. When you buy the latest Call of Duty, you play the single-player perhaps once, but it's the emergent nature of the multiplayer that keeps you coming back. In Minecraft, you're never complacent; you're always searching, discovering, planning and building. By constantly surprising the player, they always come back for more. To see what comes next.

There is no such thing as an ordered world in Minecraft. As such, when you start to master it, the sense of accomplishment is real. You don't start to control your environment because you put enough time into the game, or because a cutscene advances the story to the next state. You control it because you grow stronger through your own efforts. This is your mark on the world, your stamp.

Virality

To date, Minecraft has had over 630,000 purchases, and yet it's never been advertised. That's 630,000 people paying money for an alpha product. It relys on word-of-mouth to spread the enthusiasm behind the product. Every person that buys it talks about it. As it's all random, there's no spoilers; everyone has their own story to tell, their own personal touch to share on the game. As a game developer, you will never be able to find a more effective for of advertising that passionate users. A recommendation from a friend carries twice the weight of all the YouTube videos you can post.

Accessibility

When the Wii first came out, Nintendo went to a lot of trouble to get the console into as many hands as possible. They let people try it out and in some cases used them as salespeople to other consumers. Minecraft is built on Java and you play it through the browser. The only thing more ubiquitous than Java is Flash (perhaps with the new Molehill APIs we'll see a Flash port or more browser-based 3D worlds). You can play the Classic version for free to get a taste of what the game is like. All of this is geared to getting as many people playing the game as possible.

When the game got a lot of mainstream attention from some of the bigger gaming blogs, the surge in players caused the servers to start slowing down and crash. During the time it took to get a new solution in place, Notch, the developer of Minecraft, let people play the current version for free. The sales subsequently took off.

Often your first taste of Minecraft is the free classic version, which restricts the gameplay to the discover/building state. The controls couldn't be simpler. One left click to mine, one right click to build. This simplified control scheme allows the first-time player to quickly experience the basic gameplay, providing the hook to encourage the player to buy the game.

End

Sometimes I wonder how much of Minecraft is good design and how much is necessitated design. Random worlds are the only feasible way a small developer can provide such vast vistas, yet they also play strongly to emergent gameplay. The art style is managable, not amazing, but lets the player utilise their imagination in bringing the world to life. Lack of tutorials and instructions make the initial few nights daunting, but encourages sharing of knowledge and the excellent community around the game.

Full credit has to go to Notch for the current state of the game. I'm sure this game would have been cancelled in it's early stages had it originated in a typical studio. That, or it would have emerged vastly different (cutscenes ftw!).

So what can we learn from Minecraft? Well, we can learn that you don't need to take the player by the hand; that using the player's imagination is one of the most powerful tools in the developer's toolbox; that real fear comes from within rather than without; that a more satisfying feeling of growth comes from the player setting their own goals rather than having them set for them. And we'll have more to learn. The game is only in alpha after all.