Probably the worst colour by number I've ever played, it's just extremely unsatisfying and it's weird how the colours are actually like pictures? That you're just filling in? I don't even know how to describe it. And I understand that it's a free app so you can't not have ads but maybe not in every single possible crevasse you could think of? Like directly before and after you fill in the picture? That also takes the "satisfying" element right out of a game and can ruin the entire experience.