Great game I play it at school a lot, I suggest making it so that you can somehow give your teammates ammo or a weapon or make them pick up weapons off the group because after they run out of ammo they're useless. Great game :D
This is part 3 (final)
During this whole process don't really worry about mines they don't help that much later in the game, it is good to have one or two handy though. Make sure to also be repairing the truck and try to finish the rounds as soon as possible to get more time to regain your ground.
If you finish the game before getting all of the weapons then don't worry you can just keep going. Or just leave.
This is part 2 :D
Next on the list is the Striker; it may look like a grenade launcher, but its a shotgun (disappointing :( ). Have the second row of skills done or close to being finished by now preferably starting on the third row.
Afterwards buy the spitfire it is (in my opinion) a better weapon than the Minigun because it can go through enemy's (it is a flamer). At this point you should most likely be almost done or fully upgraded by now.
Next by the minigun and if you want the other weapons you didn't buy (they aren't that special). Be fully upgraded by now.
At this point get on top of the car shoot down the birds with the mini gun (or any other type of machine gun) then shoot the zombies with spitfire while they are attacking your car.
Here is my strategy I think it's a pretty good one it's for that person just trying to beat the game.
Buy the revolver first, it is much stronger than the pistol. Then save up your money for the uzi. Upgrading your businessman man skill is helpful for this. Make sure to upgrade your reload speed all the way while saving up money. Make sure to upgrade your accuracy at least once before this also (no penalty for doing it after either just helps to do it sooner).
Next on the list of items is the Mossberg, it is pretty good for taking down those big enemy's that the uzi takes time to kill. I would suggest that by the time you have the mossberg that the hole first row of skill's are all upgraded (the ones that require one point) or at least the reload speed upgraded to full, businessman skill upgraded to lvl 2, and the quick learner skill upgraded to 2.
This is part one.
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Haha, awesome! Sounds like a good idea to me. I'll be sure to incorporate that into the next game. :-)