Hey if you like zombies, go for it. Just because everyone else is doing it doesn't matter. It just gives you incentive to do it better than everyone else.
Don't think too hard about some convoluted backstory. Most people get bored reading a huge setup story. Just throw the player into the game, drop some hints along the way, some desperate notes from other survivors, and eventually reveal why this is happening. Again, there are only so many ways to tell the tale of a zombie outbreak, you just want to keep the player interested enough to find the next piece of the puzzle, even if it is cliche.
"bond1 - You see this name, you think dirty."
SPECS: Windows7 x64, Intel Core i7 920, Geforce GTX 580, 6GB RAM