Very cool game, the idea is unique, I think the timer should be shown at the beginning but maybe overtime it changes or disappears.
The human mode was too strong, it was better to wait to switch back when a zombie and shoot from a distance then to get close when a switch might happen,
maybe make there ammo that is dropped by people and randomly by zombies so you have to conserve ammo and as a zombie are forced to get kills.
the movement was a bit slow for everything, speeding it up would be nice.
with further progression like upgrades (maybe you get upgrades for your weaker zombie form by killing zombies and are forced to kill humans as a zombie to keep the human powerful), more rooms to explore, larger and more spawn waves, and maybe an endgame.
the bots feel very well made except occasionally getting stuck, (maybe have a panic animation/sprite for humans that are not moving).
Maybe also have it so as you kill humans as a zombie they become zombies and then during the switch some turn into people again?