Minecraft is a game about placing blocks to build anything you can imagine. At night monsters come out, make sure to build a shelter before that happens.
It's taking the Bomber and his friends by storm at the moment on both XBox and PC, though noses have been turned up at the iPad version.
You can read the story of the game at http://en.wikipedia.org/wiki/Minecraft. It does my heart good to see what was until comparatively recently a one-man-band achieving like this.