Especially when you make the run for the helicopter. Usually I start in the radio room, bar the doors and wait for the zombies to start climbing through the windows. Easy targets. Then when there is a lull I make a stand on the roof of the radio building where there is usually a minigun unless the Director chooses to forget it. This it is onto the helo pad when the thing lands which usually comes amid a horde of zombies, tanks, hunters and every other creature the game chooses to throw in your way.