The difficulty really isn't that bad. I found it easy to figure out each level. However, I believe the controls should be explained more thoroughly. I did not know how to invert gravity, for example. I assumed that since x is drag and shift is run, z must be used for something, so I figured out that z was to invert gravity. The instructions did not say this.
Anyway, the game is nice and simple. It gives us a classic puzzle-solving adventure. It could use more eye candy and some music and sound effects and so on. It could use some an undo button for when you accidentally press z a second time and lose a cube off screen. Various things need improvement. However, the overall game design is not bad, and I like the level design.