Cool game!
Here are my thoughts:
- Make it more obvious when you win a round or unlock a new door with a message appearing on screen or a sound effect.
- Have a notepad to write down the working or even the question, so that when you go exploring to find the answer you can remember what you're looking for. This could be great if the levels ever expand in the future and you have to search for a longer amount of time.
- Have hidden treasure chests (or something similar) that can give you power ups if you're able to solve an even harder equation. Something like a double jump to get past the red lines easier, or a sprint to move between levels faster.
I saw others have pointed at the FPS stuttering issues as well, but I'm sure that's something you'll be able to figure out in the future. Nice job!