Pretty freaking good.
First, the review:
It might be the best in the genre of games involving shooting the hell out of zombies, and that's a damn lot of games.
Several suggestions would be to have upgrades for the barricades and weapons, a higher possible number of survivors, last two weapons made better, more variation in how the zombies could attack, MUCH longer nights, some more varied types of weapons (I'm thinking something along the lines of a grenade launcher).
The hour allocation system is brilliant and original, don't change that if you ever make another.
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Now for the easiest way to win this game. Spend all 12 of your hours after the first day to look for survivors, if you have around 4, get a couple weapon upgrades while getting your survivors to 7, from there, simply coast through the rest of the game getting the remainder of the upgrades.
Note: you will NOT make it further than night 3 or 4 with no other survivors.