Your objective is to shoot the bad guys as accurately as possible. You can aim for the head or the body area. The closer you are to the center of each of these areas the more points you gain. The trick is to make every single shot count.
Kill all zombies before they reach the top of the canyon and wreak havoc on the citizens of Zombville. Kill them all, make money, upgrade your weapon and buy power-ups. Good luck!
Shoot enemies down and advance to the next level. As the game progresses more weapons become available and you will encounter more challenging enemies.