I'd say the zombies part is sort of secondary. The characters survival and interaction are more interesting, I think.
This. its more about the Characters then anything..
This. Nowadays Twd is more focused on the characters than zombies. Zombies are merely a distraction and they don't even play a main role in the plot. You could say they are like... Secondary characters.
It makes total sense as well, in a post apocalyptic situation like that, you should be more afraid of the living than of the dead.