I don't claim to have seen every zombie movie. I don't claim to have seen more zombie movies than every member on this forum. I do however claim that I am a big zombie movie fan and have probably seen more than the vast majority. Between high budget films to lowly B rated (and worse) ones.
Just a few things to consider.
Some people tune into zombie movies just to see the gore, to see how the zombies look, to see what new ways a zombie can be killed or to see new ways to see a zombie kill someone else. The same could be said of the multitude of Friday the 13th movies, Halloween movies and Nightmare on elm street movies. Most know going in that most of these movies are using the same basic story lines so not much new in that department but they love seeing the main bad guy and how he is going to destroy someone or how he gets destroyed. In the case of the nightmare on elm street series it turned into what new funny lines Freddy can make.
There is another factor that is truly at the heart of zombie movies that some people seem to miss and it is odd that they would miss it or marginalize it because for the most part it is, like I just said, the heart of zombie movies.
It is the story lines of how the living interact with each other during desperate and intense times under almost unbearable situations that seems to have little to no hope of changing.
The dead are walking, everyone that gets bitten by the dead wind up turning into the dead and the cycle continues until eventually nobody will be alive. However that does change in some films by either finding a cure or waiting until the zombies die from starvation (28 days later).
So the most important part, the main heart, the central theme of zombie movies is not really the killing of zombies. It is the survival of the living and the interaction with the other living. Who is the bad guy that might turn out to be a good guy. Who is the good guy that turns out to be a bad guy. The line that blurs between good and bad depending on the situations. The love or purely sexual nature that might develop between characters due to the stress involved and needing to feel some kind of hope or fellow human contact for reassurance even if it just be for a bit.
Zombies are just creatures driven by the need to feed. The living (in these films) are filled with the need to survive, some feel the need to help others even if it eventually puts them in danger. Others feel the need to survive by putting others in danger to save themselves.
Think of the original zombie movie by Romero. The old black and white version. It was not really about the zombies. It was about the interaction and action of the living that drove that movie and drives most of the other zombie movies.
The same will happen in this series.
Now sure a series and writers will sometimes draw things out longer than they need to do in order to fill a quota of episodes and keep things going longer.
Look at lost for a prime example as it was only set to be for so many seasons but the popularity of the series made the writers draw it out a few more seasons...to the point of making some of the characters that were only originally meant to be side characters and turned into main characters. Some of these characters had no past originally but they eventually devoted episodes to creating pasts for them...Hurley (sp?) is a prime example of that.
So although this series might be drawing things out longer than normal. Although they are adding more characters or devoting them more than was in the graphic novels...it is something to do to extend a series. But at the same time it is doing what it set out to do and what the central them of the zombie genre (and many other genres for that matter) set out to do...Concentrate on the interactions of the people. The zombies themselves are just the catalyst that makes these people come together to try and survive. Take out the zombies and put in a monumental weather event, cosmic event, medical outbreak event, post atomic/nuclear war event, ship wreck in a deserted area and many other scenarios that would fit and you would get similar things.
It is all about the interactions of the people.
Think of a Quinton Tarrintino (sp?) and why many like them and they get a good deal of critical praise. It is rarely about the action, it is about the interactions between the people. He has made it an art form to have the most interesting, intense, funny and thought provoking scenes as nothing more than a few people talking instead of the action.