You're doing a lot of things incredibly right in this game!!
At first when I was reloading after shooting 1-2 shots and I still lost all the other bullets I was like, oh there's a bug. But then I thought about it and realized, if I only shot one bullet and changed magazines I would have thrown away almost a full clip! It then made a lot more sense to me! So that touch of realism was awesome, but maybe re-frame it that you're changing mags and not just reloading (If that's the direction you're trying to go)
Also I love the scarcity of the ammo! I really got a sense of panic when I ran out and had to dodge the hoard of zombies to go find more!
The sounds are also really good. The ambient noise in the background sets the mood just right. The zombie noises were a bit quite though, I didn't even realize they were making a noise till later in the game.
The only critique I have left are all cosmetic. I would love to see more animations for the player reloading and getting hit, and the zombies getting hit too.
Keep up the great work man!! I'm really impressed!!