I like your game a lot! The topic of the Jam is in a very creative way implemented. The more zombies you have the stronger you are.
The art the movement of the zombie horde the gameplay is where I fall in love with immedialety. The Brackeys logo in the middle of the game really got me :) Brackey would be proud.
The only thing I can think of improving is the music. It is a bit monotonous unfortunately. But I am not a musician so I can't really say in what way to improve it.
Great Job in one week only!