Was really good and enjoyable!
Loved the math aspect and not having to do only one math equation, but it felt as though adding and subtracting was pointless, as multiplying always results in a greater number.
I also felt a bit dissapointed to see no negative numbosses (that you have to add to), and the allowance of impresision to the subtraction (when you do "16 - 24" its equal to 0 and not -8).
Also maybe some upgrades felt redundant, like positive number don't heal and positive numbers deal damage, an upgrade structure would have been better, where one turns into the other.
But overall it was amazing.