Love the idea, love the art and music, the gameplay is where it falls a bit flat. The biggest(and really only) problems are that sometimes I have no idea how far away the cursor is, and trying to change height is really annoying. I would probably suggest using Space and Shift to ascend and descend and using a raycast from the crosshair to the nearest surface for placing blocks. A few simple fixes would take this from a pretty albeit somewhat frustrating game to a really fun experience!