This is very cute! I'm surprised something like this hasn't been done sooner.
I lack much criticism as this game feels like it has done what it's set out to do. I only got suggestions that I would like to see such as maybe letting the character hold a prop (could have them holding Alien Hominid's gun, for example) and picking different colors for individual parts, like clothing and hair. I think that would help people to make their TRULY unique Picosona.
Again, cute idea, and can't wait to see how you build upon this!