Great idea!
Gameplay is simple, but it doesn't make it very boring. Graphics are nice, controls are intuitive and responsive.
Story in the beginning is very creative, loved how you used the theme!
This game needs just a little more diversity: other types of zombies, cars, or something like day/night cycle? Because, yea, it keeps your attention for a while, but after some time you just stop feeling any competition, which, at least for me, drives me to play game more and more and spend a lot of time replaying game.
So, overall, wonderful game, would love to see your other projects in the future!