I love the visual feedback when you are done, or like when you have a mistake - (the critters being sad).
The whole look of the game is very polished and well done! I would make some minor bug fixes that I saw were already mentioned and I would disable the option to click on a tile and show a critter even if none is chosen atm.
I got so many mistakes because I would click on a tile and it would just put the top critter there even without being selected!
Overall, well done!!!