:D I'm afraid it's just a lot of programming experience. And man, Unity is a lot less painful to iterate on than Phaser was. The feedback loop from their editor is just so much faster.
Thanks for the feedback on difficulty! I wasn't actually trying to target kids, but I did try to keep the puzzles fairly simple. (Most puzzles require moving just 1 letter, as you noted.) I was worried that it'd get frustrating if I made it much harder...but once there's some sort of hint/skip system (as others have suggested), that should balance out nicely. Thanks for the push to make some harder chapters.