The thing about zombies, is that there's just not that much to be done with them. Take the pivotal Romero zombie series, what made the first 3 entries so great was the social commentary in the situations. After that, the series just turned stale, not necessarily because romero lost his touch, but more because there just isn't that much more to be done with zombies, other than making them explode in more glorious ways.
Maybe HSotD does have something to say. Of the first few episodes i saw, i felt that i saw it all before. Which is perfectly all right, since I can enjoy zombie movies. But zombie movies usually don't run for 13 episodes worth of content. What it comes down to, is that the protagonists in general of such movies/shows are just not important enough to care about, such that you would want to invest that kind of time watching.
On another note, shows that are like 90% fan service tend to suck. Just because the director made the fan service the focal point of the show doesn't make it not suck. Just because there are zombies, doesn't make the show magically good.