Without spoiling anything, let's just say that there's a quest in Sunday's episode, a quest that I didn't think the show would convince me was necessary. Yet eventually I understood why it was necessary, to Rick, anyway. The episode is a morality tale of sorts, but the story is told with a light, sure hand (and there's not all that much violence, as it happens).
As many others have pointed out, zombies are really just shuffling, flesh-eating backdrops. They are not intrinsically interesting in and of themselves. What they do is shine a light on who people become during a deadly crisis. Do they try to grab power? Retreat further into themselves? Exhibit selfishness or altruism? All the values people think they possess aren't truly tested until there are flesh-eaters on the streets; then it becomes a whole new ballgame.
Just as alcohol or drugs tend to bring out qualities that were already there in individuals, stories about post-apocalyptic societies struggling to survive are about the moral and ethical compromises people find themselves all too willing to make in times of trouble. The element of surprise doesn't just involve zombies popping up here and there; if the story is working well, as it is in 'The Walking Dead,' the audience can also be surprised by what the characters are capable of, and by the ways in which "civilized" people can quickly revert to brutality (or traditional gender roles, as one character notes in Sunday's episode).
In these kinds of stories, over time, the question evolves from "Will these people make it?" to "Should these people make it?"
Of course, at this stage, Rick isn't an ambiguous anti-hero a la Vic Mackey. 'The Walking Dead' isn't that kind of show. In such a bleak and forbidding world, the audience needs someone to believe in. In Sunday's episode, 'Tell It to the Frogs,' we learn more about why Rick might that kind of guy, and you may start to root for these people -- some of them, anyway -- to survive.