Wow, really cool! this reminds me of BASES LOADED which i also enjoyed a lot , but this game seems to have a bit more balanced upgrades and a lot of future potential.
the 2 things that stuck out to me and felt a bit off were the zombie spawning and exiting shop. i feel like the gravestone sprite should flash white or something right before its about to spawn, so id know if i can make it over it. also feel like there should be just a slight pause after exiting the shop, to give the player some time to react, I did get used to this after some time, but like a 0.5 second pause would really help.
Defenetly going to check out the full release i the future, for now a solid 9/10.
:)