Well crafted entry, and with no engine game engine behind, quite impressive!
The sprites and animations are very well made, I find specially good the death animation for zombies, it's both smooth and satisfying! 🤤
The game's a little buggy at parts. I guess that you had to write down many of the stuff that an engine already gives, and I value that, but you can easily get stuck inside Robert, or worse, between Robert and a tree (it happened more than once to me in my playthrough, damn my luck!). Also, there seems to be some kind of bug at the end, I entered the final zone but I didn't get the screen showing my time 🙁.
I have to admit that the playability did not click with me. It's a 100% design choice and totally subjective, but I totally prefer a Hotline Miami style playability in top-down-shooter games. I found myself fighting more times against the controls than the zombies hahaha! But as I say, it's just my POV, the game's fine as it is, and I understand why would you choose this control scheme for the game.
I don't fully understand why some zombies die in one hit. My guess is that it's just random, but sometimes it felt like it was because I was aiming directly on the zombie. If it's just by chance, I would like to suggest adding a mechanic where you instantly kill a zombie if your cursor is in the zombie, this way you reward players for their aiming skills, and it makes some parts more manageable!😛
Other than that, the game's quite well crafter, it shows quality and skill! Good job! 😁