I don't think that this movie knows what it wants to be. It wants to be a zombie movie but not enough time is spent killing zombies. They are a dangerous element that exists outside but not much of a threat indoors. Although the characters are forced to go outside eventually, the build-up to that decision happens much too quickly. The whole thing just left me with more questions than anything. How do you survive 20+ days with barely a week's worth of food and no water? How does one watch the news on their television with no electricity? How do you post videos online when there's a network outage and simple messages aren't even coming through?
Anyway, as far as zombie movies go, I would say that this movie is okay.