The King has arrived.
Fantastic work. I love the detail that you put into the game. The painstaking work that must have gone into the combat, the unit designs, and then to top it off you put effort into your sound design.
This game is the best Zombie flash game on the internet, and you've created the gold standard to which all other flash game makers (not just Zombie games) should aspire to.
You really did a great job not only creating a compelling atmosphere, but you also covered well above and beyond the basics of Zombie survival.
The only things I can recommend in any sort of sequel or future flash production are that the machine guns felt imbalanced. i could mow down more zombies with a Uzi than I could with a M-16 or a Ak-47. And the Chainsaw.... really fun, but ultimately broken. I would recommend that given it's high ammo count, and it's high damage, make it unreloadable. So then players couldn't just pick things off, chainsaw the zombies, and repair the 20 points of damage each round.
I would also love to equip the survivors with weaponry (instead of just hoping to get a guy with a rifle or Magnum).
I also found myself forgetting to check the journals, so you might want to make them more apparent, or put them on as apart of the background.
I loved the stats, but they felt shallow. I also disliked the time limit of 20 days. Perhaps as your survivor count grows, in the future you would have to manage more stats. Such as Ammunition, food, materials, sleep, etc. Just a thought.