Minecraft is a game without many rules. A sandbox where you can do what you want. If you get bored by unlimited freedom, you can turn on game play mode and fight zombies while you dig and build.
Minecraft (thanks Notch for this creation) steps aways from other genres to give the player a free for all sandbox to play in. It has been in development since mid 2009 and its a simple concept without many rules and without goals. The player lives in a 3D virtual world, with or without friends, and mines 1 metre cubes out of the ground with the ability to build things out of these cubes.
Gravity plays a small part in this world, with the rule where you you just can't put things in the air. The blocks have to stick to other blocks either up, down or sideways, but then you can remove that original block you stuck it to and you do have a block in the air.
There are a small bunch of elements to dig, chop or hoe for, including rock, wood and heavy minerals. You can also change these elements into many other things, like tools and switches, either individually or by combining with others materials.
Initially I played the game mining for what I needed and going by the rules of this world. I then found that I could have as much of what I wanted just by asking. That gave the game a whole new dimension and I was able to start building anything that I wanted out of the limited amount of colours that I had in this natural world.
You can take if further and work in complete design mode with many more materials available, but I have found that I am in a nice place with a few friends and our little world is growing all the time. I am just not wanting to move. The world is also infinite in size. As you explore, the world gets created "beautifully" in front of you.
Following are a collection of screenshots from the game on our server. You will notice that the blocks are large, but in the end, that is just perfect for a balance between too much fine details and hard work, to coarse and granular but quick and easy and most of all "FUN" to build.
Minecraft - The Sydney Harbour Bridge
This is, to date, the most fun thing that we have created. The Sydney Harbour Bridge. A national icon and also great to look at and a wonder to build.
It only took about 10 minutes to design, just taking a plan from the internet, shrinking it down to 1/4 scale in pixels and then blowing it back up again. Just pick which pixels you want filled and which not to.
The build took around 5 hours with 2 helpers.
We couldn't build it to scale, as we would reach the sky (64 blocks above sea level) and we didn't want to dig out all the water. So this model is 1/4 scale of the real thing, in this virtual world.

Nearly finished. There is also a cruise ship being built in the background.

Day view of the bridge

Standing back for a look. Not bad for only 30 or so blocks high.

Construction worker busily on the bridge.

The first car crosses the bridge.

An isometric map generated of the area.

We step back to look at our creation.
Minecraft - the Natural Environment
A great thing about the game is the natural environment. You can take a blank world, or you can carve into the natural world. There are many great wonders to find just by exploring both above land and below the surface.

Love this spot. One of the first that we found. Seemed so far away from everything on the map when found, but now a central part of our civilisation.
The first day one of us managed to kill the waterfall. I was devastated. We did manage to fix it a couple of days later once we figured out how.

Another view of the waterfall area.

Trees can just grow out of control. Something to do with growing them near light apparently.

Trying to control lava and water. Oops, looks like someone is on fire, again.

Sometimes you get a glitch in the matrix. The ground hasn't rendered yet, so I can see all the cave structures below ground.
Minecraft - The Community
You can have a community in Minecraft if you want. There are public servers or you can easily build your own private server. We have a private one. It is a small group and we enjoy building together and also keep out of other's creations.
The public ones do have problems with "Griefers". That is when someone dumps a lava flow over your creation, or floods the place with water. I had those problems for about 10 minutes until I joined this private server.

Here we are just after the bridge build. Squid sees it for the first time.

AFK. Don't go away from your keyboard for a long time or you may find yourself buried, at the bottom of the world, in Lava or Water, and without Op access to tp out.
These are not natural things that happen to you, but more of what your friendly players might do to you.
Minecraft - A Castle
Building out of blocks quickly leads to building castles. It must be just a natural part of our genetic makeup. We have a couple of castles in our world.

Looking up one of the towers. It is great the planning and thought that happens when building.

The grand entrance.

The grand entrance started from building out of a path under the water. Its tough work building under water, as water has flow.

The courtyard. Creating images block by block.

Castle dining area. This is on the third floor of one of the castle sections.
Minecraft - Other Creations.
I have so many ideas of what I want to build. I find each a unique challenge. Here are a collection from around our world that I and others have done.

Sphere. Had to conquer the building of a sphere. This one is 24 pixels in diameter.
This sphere is above a pit of the same size that goes down through the water and all the way to "adminite", the bottom of the world.

Building a tunnel under water. Quite a feat, as water has flow and also you can't breath it (though we are immortal in our world).

Christ the Redeemer. This spot looked like a great place for a huge statue overlooking our landscape atop a great cliff edge.

The Great Wall. Just starting to traverse the landscape. In an infinite world this could become a problem.

Another bridge study. This is part of our expanding road matrix.

Interconnecting our creations with a road system.

A first creation, now an eyesore. "Look, I can write my name in stone". Hmm... better do something with that soon.
Minecraft Stuff

Here is the list of materials that we currently have access to.
Links.
Minecraft official site.
http://www.minecraft.net