Greetings, Tekamutt.
We appreciate that you enjoyed the game and, of course, that you took the time to point out our mistakes.
Yes, following other comments and feedback, this issue was raised—specifically the lack of UI implementation across the scenario. Given the variety of weapons and interaction methods, UI is a fundamental aspect of the user experience, and we will certainly keep this in mind for future projects.
Regarding the hitboxes, the situation isn't exactly as you described. Damage output varied depending on the weapon and the specific body part hit. Also, the large zombie has the most health; some weapons simply weren't powerful enough to kill them on their own, so using explosives was one way to take them down.
You are right, though—we really should have implemented visual and audio feedback for the weapons or upon impact with the zombies. That would have made it much easier to tell when a zombie actually took damage or when a weapon had fired.