A decent cod-zombie like game. Try to add your own twist, else it becomes a poor version of "cod zombie mode". The first things I can think of is more interesting weapons, different enemy than a zombie, power ups that player can pick up etc.
The style is very fitting for the game(well done). But I struggled to see where "built to scale" comes in?
Besides that, well done! I love when I instantly know when to do, and it was easy to know here :)