It is a blockworld RPG game (like infinminer and minecraft) where you can move around an infinite world and build anything from castles to cameras and trapdoors.
It has many unique features such as its dynamic book system and scripting console as well as many other things like cameras, trapdoors, paintings, complex crafting and much more.
It also gets updated every single week with new features based on what the community wants.
Best of all it is free to play!
Please give it a try and let me know what you think I could add.
Zune Marketplace Deep Link
CraftWorld on the zune website
Note: These screenshots are from the first version 6 versions ago.