Left to Die
It is a mission that has gone wrong. Nobody expected that a zombie apocalypse to happen. A soldier was sent to rescue a priest from the hands of the rebel. This soldier was tougher than any soldier that is already in the battlefield. On his way there, he fell down and when he woke up, he was chase by undead. He have no choice, but to run non-stop. Soon, he got fortunate as there was a military camp nearby with all of its weapon. He can use the weapon to defend himself. The soldier know that it is not his time to die yet.
The game is played via mouse and the idea here is to defend the stronghold from the ravaging undead. Each kill would earn you money and you can use the money to buy upgrades. You can fortify the defenses, or buy a better weapon. Either way you are prolonging your life. As you make some progress, the zombies would be tougher. There would also be a boss fight and the only way to defeat him is by shooting him on his weak spot. If you can't hit the weak spot then he would call forth his undead army.