The brilliance of this story is that it gets at what makes really great apocalyptic fiction. With a few exceptions, most modern apocalyptic fiction is about how scary the zombies are, or the mutants or the monsters or whatever. The brilliance of classic apocalyptic fiction, the Wyndham era, is that the mosters are just background to the horror of how human beings treat each other when society collapses (and in many cases, the tenderness and humanity of which humans are also, in contrast, capable). This is why 28 Days Later was so compelling to me.
What makes this human element important is two-fold. First, there's the element of realism that was mentioned in the intro; anyone who has seen how people behave after natural disasters, or in wartime, or anywhere where the usual way of things is interrupted knows that this is where you truly see the heights and depths of human behavior. Second, I think it just makes the horror so much more effective. When the scariest things in the story are the zombies, you can console yourself that there's no such thing as zombies (at least in daylight
). When the scariest things in the stories are the people next door, at least when driven to extremes, you've got something very real to be scared of....