Good weapon combo: a semi-auto/automatic (e.g. AK47/Uzi) + chainsaw. Having an automatic gun is important; even if the shots miss your intended target it will probably hit someone behind. And the chainsaw can help you clear the zeds near the barricade. And if the barricade fell, a close range weapon is crucial, as you can instantly kill the zombies that come too near, and hopefully survive another day.
Perhaps the reason for the more people you kill in an area the more infested it becomes is because the story takes place where the apocalypse has just started, and people are turning into zeds left and right. Therefore, the longer you stay in one place, more locals are turning into zeds, thus the danger increases... And the zombies are swag walking around... *shudders*
I get chills every time I revisit this game and hear the music... It's been a few months since I last played this game but I shall always treasure it in my heart. It is, in fact, the best RPG I've ever played, right at the top. I just want to say to the developer that, even though the game is not finished (and I'm not gonna pressurize you), that you have done a simply brilliant job on this game... I always wonder what happens after the game ends though...
Could you at least tell us the whole story? Better yet, you could make a Part 2 and start a new Flash file. That way it (hopefully) won't take ages to load.
At last, a big thank you to you, Douglas, for making a game that I would remember forever. Give yourself a big pat on the back!