Tried it, mostly repeating the things already said…
Died a few times before i have figured out the controls.
I'm fine with WASD, but i would have expected: If you can aim with mouse, you also can shoot with mouse.
Though, i think there is no need to move at all. You can just stand in place and shoot them all before they get you. I did the same as a kid in Asteroids on Atari and could play for infinite time this way. So i think it's a design flaw. If you can move, there should be a reason you have to move. Obstacles could provide such reason, but then you also need some basic AI. Powerups would be another reason.
There are big issues about fairness: Zombies appear exactly at my position out of nothing, and i die before i notice what's going on at all.
And also: Multiple Zombies spawn at the same position. I shoot one down i assume i'm done, aiming for another, but then i see the zombie is still there although i did hit him. That's because it were actually two zombies.
Such confusing things should never happen.
It's too fast paced from the start. The player has no time to realize the situation and think about some strategy.
You could make them move slower initially, and make sure they spawn at some larger min. distance to the player but also some smaller min. distance to other zombies.