Cool idea. I liked the graphics and palette, and the gameplay was easy to pick up. Though I would have liked the zombies to be less clustered into a single area, to make it seem more horde-like.
Also, I seemed to win when somewhere offscreen sometimes. E.g. I'm just picking up zombies and then I suddenly won. Are the non active zombies killing people? Or is this a bug?
I'm wondering if this could be a bit more varied with some linear level design -- i.e. having specific kinds of challenges set up for players, rather than just having them roam around a mostly open area. (Though that's perhaps beyond the scope of the jam.)