It's a really cool game, and definitely has a healthy amount of "Juice". The controls are simple and feel great to use, but the zombies really like to overlap with one another which takes away from feeling like you are assembling a horde. An easy way is to add colliders to each zombie and let the physics system handle it, but the performance can't handle it, you could look into using a boids algorithm to manage pathing and separation. Overall great job!