It took a short while for me to understand, but once I got it, it was really addictive. Very polished and well thought out. I haven't quite finished it yet (I spent way too much time on it and I needed to move onto other games!), but I think it was interesting to see new concept being added gradually, and subtle differences in vibe between each level created through music and texture overlay. I felt the undo feature was a nice touch too.