Thanks for the feedback!
Definitely, there are some balancing issues. If possible, I'd like to expand the quest in the future, meaning that players have more possible upgrades and more waves to defend. So that the difficulty curve can be smoothed out.
It doesn't sound condescending at all. I'm still a beginner in designing these kind of levels. Any feedback is welcomed!

[Shushumu]
I wish you the best on designing!

Honestly, I thought it was too easy. It may have been tweaked by now, I see the post is from december, but when I played it, I made 1 upgrade to the safezone. Then I talked with the commander. Not knowing it was going to be the end of the mod, I just kept talking with him and spawned the zombies. With no upgrades at all besides the one you have to use during introduction, I managed to defeat every zombie with minimal effort. Then it was game over and I was confused and wondered what happened with all the other upgrades ^^.

I love this idea, only thing I have to say is that it should maybe be more obvious that starting a horde means mod final. Like a text showing up saying that "If you spawn the hordes, you won't be able to come back to upgrade the safezone anymore" or something like that.