LOVE the idea, and the presentation and polish is breathtaking. How on earth did you have time to get such good soundeffects, art, animation, an undo move system and music all whilst making a rather complex game?! Seriously impressive.
I found the last few levels a bit too hard imh. I hadn't really learned how the expression ordering worked, especially when one calculation is at 90 degrees to another. I think maybe there should have been a little more time spent on teaching those mechanics (still i can't blame you for wanting to put in fiendish finishing levels, you'd earned it by that point!)
Really well done, and I fully expect to see this game in a GMTK video not long from now.