Ohhh brutal, I love it! :D
Very simple gameplay, which is however pretty fun because it feels so satisfying. Seeing that this is in the Novice category, I'm not sure how many games you've made before, but if this was one of your first, kudos! It is already looking really professional! So let's talk about some things:
1. Bugs
I've encountered a few smaller bugs like one blood particle moving along with the player because it is probably a child in the hierarchy, me being able to push zombies shortly before they spawn, and some other small ones, but the very big one was my HP: For some reason, I was sort of invincible for a minute? My score was around a thousand when I realised that a zombie didn't damage me, so I tested it out and when there was a mass of around ten zombies, all attacking me, I only started taking damage after a minute or so. In a survival shooter this is definitely something to avoid. No other major bugs though.
2. Graphics
Cohesive, look cool and the animations feel smooth. Very good job. Maybe a bit of diversity on the blood particles could be added, but definitely kudos to the artists.
3. Audio
No music, which is kind of a shame. Maybe something "Doom"-esque could fit, seeing that you're massively better than the zombies. The audio is simple but fitting. You selected good sounds that match and don't get too annoying. The only sound that didn't fit for me was the zombie hit sound.
4. Gameplay
Like I said, I had fun! Reminds me of a small arcade shooter. The only thing I would definitely change is the difficulty. I don't know how the spawn rate changes, but I'm guessing you're incrementing it bit by bit? That's a good idea, but it is way too slow for sure. The first three minutes are hilariously easy. Also a zombie variation would be nice, maybe an exploding zombie that moves very quick, forcing you to cancel your focus on one particular zombie could make it more interesting. A landmine? Definitely a lot of potential.
=> Overall, a fun game, which has one major bug and could be more difficult. Good job!