Sorry, there is one more thing I forgot to mention. In my respectful opinion the game is much too easy. Having an update to add a new difficulty or new types of zombies in the sequel would be a great addition to the game!
Very well done game. The fact that the city is randomly generated adds a good amount of replay value. I have several bits of constructive criticism: While there is a wide variety of melee weapons they all do the same thing and have the amount of damage (as far as I can tell). Also when you get 4 guns there is no sense in having a melee weapon so perhaps a buff to the melee weapons would help. And last but not least instead of having C as the only key to change weapons you should map them as 1-4 or Q for the previous weapon and E for the next weapon. Great job though, Keep it up!