I remember how I used to draw things in the air a little myself when I was little. I can not hate this game because everything is just done really well. It seems to be exactly what you would envision in a game that features invisible ink. I still can not help but say that I am just not good at this game at all and needed every hint just to get past the first level! At least you were nice enough to have different degrees of difficulty. The best way to figure this out is to probably get yourself a pen and paper and draw it out in real life.
There could have been some more perks like maybe some more sound. The artwork that you could see (with the pencil) was at least very well done. It was also nice to play a game that seemed to truly have originality. I suggest everyone to work on the easy levels at first. This is a game that really requires an active imagination.