Made me a bit nostalgic because it reminded me of those old flash zombie games.
It was fun but my main criticism is that it was too easy. Pistol needs to have a limited fire rate, player is too fast and there is too much ammo of the strong weapons like the rail gun(which felt very satisfying when I lined up a dozen zombies and killed them with 1 shot), so wave 7 felt just as dangerous as wave 3.