It took me quite a long time to work out how to play. I really appreciated the onscreen step by step instructions, but actually the first step is to pick up a monster and put it in the tub. So I was clicking the sponge, changing the size, and clicking on everything around the screen trying to figure out what it meant by 'spot'!
Once I figured it out, I was able to clean lots of dirt from the monsters. I really love the art style, a minor annoyance for me was the sound effect when you correctly scrub a monster, it was a bit repetitive after a while.