Great game. My only complaint is a minor one. I like being able to place zombies in their respective vats preemptively. However, when you unlock the boss zombie, you lose that ability. Now when you tap on an empty vat with insufficient zombies, you are given a pop up to instead hunt the boss, even when the boss ISN'T available at the moment making it very annoying. Maybe have this pop up only occur when the boss is available, acting as a friendly reminder to go boss hunting ASAP.