So... Minecraft, yeah. I think everyone of you heard about this game (the ones who didn't now will).
Minecraft is a sandbox-game. That means, that everything in the world, you enter, can be changed by your hands (axes, shovels etc.). The world is made out of different types of blocks.
Here is a Screenshot of a world.
As you can see, the graphics are not Crysis-like, but the gameplay is just awesome.
In this mode you start a new game and you generate a random world(which is REALLY big). The first thing you usually do is to hit some trees (you really have to do this ;D) to get some wood. After crafting (creating new items with wood, stone etc.) an axe you can get wood more easily. Then, when it gets dark, evil creatures like zombies, creepersssssssssss and spieders spawn. 'Till now you should have build a little house or something, to be safe!
So you live your life with zombies, creepers, pigs, stone, gold and with a little luck even diamonds, and you build your world.
If you haven't played it yet, don't play it, because it's really addictive!!!