I think it's good so far. Although, we will have to wait and see how well it pays off the drama it is setting up. The longer it continues, the more the series is going to have to get into the nitty gritty details of how people are surviving.
From what we have seen though, I can't pick out any major flaws. It's great that they aren't afraid to kill off characters. The only characters that annoy me are Barbie and his girlfriend. Those 2 are made out to be the overdone stereotypical heroic TV character that the audience knows can't be killed off and can't surprise the audience by going bad. Everyone else is either young enough to surprise us with stupid mistakes OR their loyalties are ambiguous enough so that we don't really know what might be going through their head.