The concept is that you are a tombstone (so you're constrained and things are out of your control). You are supposed to get out of the graveyard to reach the city gate before the other tombs and zombies destroy you.

The things that you can't control is the direction of the gun it shoots in a parabola. So you often miss the shots making it difficult to kill the zombies. Colliding with zombies also makes you lose the health. If you touch other tombs along the way, they start duplicating and you lose health. 

Yes it is possible to move the camera. I'm sorry there are too many objects nearby which makes it difficult to move around and for the game to render without lag. Hence I recommend using windowed mode and this settings I described (or lower) for best results.

Also, yes, enemies die after 4 shots. But it's not possible for you to get your shots fired at them directly because the players gun position is 'out of your control'.