Recently I discovered a funny little game that has kept me entertained quite well. The game is called Minecraft, and it is a sandbox construction game that involves players creating and destroying various types of blocks in a 3D environment.
The game looks very simple, but has a lot of features that make it 100% kick-ass. The basic idea is this: You spawn in a world, all alone (or so you think...) with nothing but your bare hands and some clothes. What you do from then on is your own choice, but as soon as the sun sets, skeletons, zombies and other monsters will come; and they're hungry for human flesh! The only way to survive is to use your creativity.
For example: to make tools or weapons you need wood. How do you get wood ? well... by punching a tree, of course! With the wood you can make some simple tools and weapons, but they won't last long. So you can use your wooden tools to get stone tools. You can use the stone tools to make iron tools, iron tools to make gold tools, and so on.
You can play the game in either stand-alone in single player mode, or you can connect to a multiplayer server for some co-operative fun. I run a multiplayer server, where I play with some friends. I've fabricated a little script that renders a 3D isometric map of the world every hour. You can view the map at http://mc.ajira.eu/, or... if you happen to own a copy of the game, connect in multiplayer to mc.ajira.eu, and you can walk around and see it for yourself (sorry, guests are not allowed to build).