Writing a story isn't as easy as you think, in fact, the process is quite fascinating. You just can't be one dimensional when it comes to topics that have been explored time and time again. For instance "People fight the zombie apocalypse" isn't half as interesting of "People fight with their neighbors while fighting the zombie apocalypse". This movie apparently takes the later approach and expands on it with a comedic element.
I love the fact that this takes a darkly comedic approach to the topic. I can't imagine myself or my friends being in some bad situation and not cracking jokes. It's just what we do.
As an added bonus, am I the only one that thinks that the old guy looks like Rick Grimes from the Walking Dead in about 40 years? Have a peak at "ZOO".