the music sounds good and graphics are ok too but you should have put some extra difficulty on waves to make the game more challenging. I also like the fact that the picture on the wall have 12x more color than the whole game :)
I guess this game could fit any theme. You just name the blue pixel whatever you want :) This time it's trusty calculator. I was expecting a bit more from the title. Theme put aside, it's a nice little game. But the waves differ only by the number of zombies, not by difficulty.
I thought this was a game where you actually use math to kill the zombies but I was sorely disappointed. I loved the pixel art though and the game itself is not too bad (and maybe a bit too easy).
But I did not find fun.