Very cute game! I'm not too familiar with Picross, but I easily found myself getting addicted to this game and going through puzzle after puzzle. I did find it a little silly how some of the puzzles would resolve (really, those two dots and a line is Pico? it could be anyone!) but it was all in good fun. And what a huge amount of content to go through! It's almost intimidating how much there is, haha!
My only major complaint would be that the controls can be a bit confusing. For example, I want to use the mouse because it's more intuitive to not only click squares, but click the big buttons on the right to change forms. However, using the mouse can be bad because it doesn't let you do tricks like being able to hold the button to paint in succession like keyboard allows: you need to click each time, and that doesn't help my carpal tunnel. So, I use the keyboard, but then I have no idea how to change forms because the shortcuts are difficult to remember: call me dumb if you like, but it'd be nice if maybe the keyboard shortcut letters could be right next to the form buttons as a reminder.
Other minor complaint would be that I feel like it could use a tad bit more juice: you know, make the title screen a bit more animated and so on, and that there were some typos here and there, but overall it feels good. Well done with this one!
EDIT: yayyy i finished my puzzle at Hard #44, thank you very much for that