Deceptively deep and well thought out, but yeah my only trouble was that the zombies are too strong early on, and building was kind of tough to do without placing the walls facing the wrong way...
I also think the trees' foliage sprite needs to be a different color or more saturated or something; I get you were going for a desaturated / grimy look but the trees kind of blend in with the ground and make it hard to tell what's what sometimes.
Also random idea but I feel like this would be the perfect game for an animal sidekick of some kind . . . it fends off the zombies while you build, etc. I thought that was what the tutorial dogs might be but I guess not, haha.
Anyways cool game, yeah I hope you can replace the menu images with something that fits the game better (maybe a better title too?); best of luck with developing this further!