Just camp on the ammo store, spam clicks and "e"....
Ugly game, good concept.

Hmm, so this is a kind of TD, except the towers defending that "Node" is you. Nothing too innovative. I wanna ask, why did you use Unity Player for this? I guess Flash could have worked well, too. No sense of upgrade at all, buying some armor or health is not necessary, IMO, because you wouldn't play this more than 5 minutes. The Ammo is very, very low. And if you can't accumulate the necessary amount of money to buy an Ammo Vendor, then you're screwed. You've got to go through those pipes where the Zombies come from to reload your pistol. Since you have only one cartridge of ammo, considering the zombies die so hard(2-3 shots), they are gonna pile up at some moment, and kill the Node. Improvements? More weapons and at least 2-3 starting pistol cartridges.

Very fun! guns need more ammo.