The Walking Dead isn't about the Zombies.
Sure there's plenty of flesh eating walkers to contend with but I really think the appeal of this series is that it's a metaphor for the end of the world in whatever way it happens to manifest itself at some future point in time, and that interests many people. Think Baltimore or Ferguson on a national or worldwide scale that goes on for months or perhaps longer...a total breakdown of society if you will, no matter what the source.
It's appeal is more, to me anyway, about how the characters change and adapt to the changing world around them that is totally out of phase with how things used to be. And of course, who wouldn't just love to do some zombie head shots?