Zombie Themed Haunt

Okay I know the whole zombie theme post apocalypse theme is a little over used but I like it a lot. I was wondering how I could make it more original and stand out. what have you seen in other haunts that had similar themes that you liked/disliked? What things worked or didn't work? What would be a cool backstory to go with this theme? I am kind of set on the zombie theme because that's what all of my props are based on. Thanks in advance for the feedback!