Great start!
Its cool, but it could be so much cooler. First of all what irritated me was the gore of the zombies. After a day or 7 the zombies were hard to spot because they have like te same colors of the gore on the ground. What would help was an other color scheme for the living zombies & the pointer.
Next you could make multiple levels. Each one with its own objective (get to point B. Survive for X min). In each level you would be able to find weapons etc etc.
K maybe i stole this for the last stand. But you could use survivors to help you in your battle. Like henchmen.
As i said in the title. Its a great start for a game that would be awesome!