Puzzle Game "How Many Blocks?"

[ozooxo]

"How Many Blocks?" is a small puzzle game I made which challenge the player's 3D imagination. It asks you to imagine 3 dimensional block configurations from their 2 dimensional projections.

Here are the questions I really want to know from you:
-- Is there any game similar to this?
-- Is the current user interface easy to understand?
-- Any other comments or suggestions on user experience?

This game is under the LGPL licence. It is written in Python+Pyglet. You can download it from
https://sourceforge.net/projects/howmanyblocks/
https://github.com/ozooxo/HowManyBlocks

There are some screenshots so you can know roughly what this game is about.