I love this! It's like cookie clicker but with zombies!
Ran fine in the browser for me (Firefox on macOS). A love how as you upgrade the zombies and the people, the graphics change too. And the hand-drawn style all fits together very nicely.
Are there sound FX? I didn't hear any, but then I had my sound turned down a bit because I'm playing in a public place. :) I'll try again later with earbuds.
Great job!