You can exploit level 11 by falling "up" onto the platform, jumping to the left and just grabbing the box from there without even going up the blinking steps. Is this intentional?
In level 12, I somehow walked right past the door and came out underneath it the first time... But then I tried again and passed the level, lol. Weird.
The control scheme was a bit awkward... I would have preferred movement with left and right arrows, jump with the up arrow, and space as the "action" key. You could have it switchable to W/A/D/Space for lefties.
That being said, this wasn't terribly difficult for me, but still managed to be stimulating. There were some pretty clever solutions to some of the puzzles, and the concept is pretty fresh (meaning that I haven't seen a million other games like this, yet). Kinda reminds me of "Karoushi" though; perhaps there was some inspiration, there?