I very much do like that the game has a gameplay loop and is indefinitely playable! :)
The most important thing missing in my opinion are explanations for how you can spend your money / showing the keybindings somewhere. I later saw you have an explanation for that on your itch page, but having it in the game itself (either at the start / in a start menu, or as an overlay in the main game) would really help!
The graphics are nice, but the park itself feels a little empty, with nothing but trees in it. I think small things like benches or something, that you could also use for tactical cover / to run around, would really add a lot of extra flair to it!
Also there seems to be little feedback on how much health the zombies, your allies or your turrets still have, which would be helpful as well! I know the screen could get cluttered really quickly when everything has little health bars, but you might also do other visual indicators, like changing the hue of the texture to a more red-ish color, or making them have visibly different walking animations to show that they are hurt!
Last but not least, I didn't see a clear connection to any of the subthemes. It definitely fits the apocalypse theme in general though.
I hope that feedback helped you <3