Infinite ammo.
The fastest route is often the most dangerous. In this post-apocalyptic world where nobody sane would dare to enter into the infamous bandits lands, home of the bloodthirsty gangs. Here is exactly where you enter with your big guns and some granades, keep the invaders away from your train, shoot missiles, explode bombs in the air and fight until the end, 30 levels full of adrenaline, 16 different types of invaders in the sky and in the earth that won't stop for anything.