Wow!! Very impressive and satisfying to solve. But that difficulty curve hits fast! I'm familiar with and enjoy math crossword puzzles like this, but for a general audience where you might be introducing this to gamers without that experience, the jump to Level 2 with so little pre-placed operations could be a very, very big jump. Of course, I can't speak to whether you want that wider audience appeal or if you know your niche. Maybe you already thought about that, but I wanted to share that perspective. I did end up needing the hints as it went along but I stuck it through and really liked the sound design for dragging the squares. I know that's a small little detail but it was satisfying.
Excellent job!!!