Very neat game for a demo, the design is cool, and I noticed that the enemy in the 3rd level was a stapler, and that was a clever addition. However the difficulty changes too subtle from the 2nd to the 3rd level. It was so frustrating that I gave up. Try make first levels a bit easier, but don't make it too easy that you can just take 2 steps to win. Make a difficult that is hard but not frustrating.
Other than that, I'm awaiting for the full version!