My first comment has to do with the reason for the blackout that was posed: a cyber attack. To me, that is pretty much nonsense. To the best of my knowledge the electrical grid is not set up in such a way that it can be hacked and taken down or, even if it was, could not be turned back on in short order.
I would say that any event that is able to take down the entire electrical grid and keep it down would be something more catastrophic such as an EMP strike or a massive solar flare event. Perhaps a very massive and very well coordinated attack on electrical substations that involved the destruction of large transformers but that seems unlikely since it hasn't happened yet. I mean, if AQ was capable of it they would have done it by now.
But, the civil unrest that was featured would be characteristic of an economic collapse and that does seem likely for reasons that we need not go into on this thread.
There were several other flaws that I suppose the film makers thought they had to include to tell the story. Notably: Using the video media to tell the story well into the blackout. First of all, their emergency power would be gone in a couple of days at best and even if they had power for weeks, who are they broadcasting to? That and the seemingly unending power that people had available for their cell phone video recorders. And honestly, even though there are some people who do document everything, who has time to record when you are running for your life? And wouldn't you be saving your battery power for essential recordings or something?
But those are minor criticisms.
On the plus side: I got a kick out of the metrosexual boyfriend who beat the guy to death with his one can of peaches. That was darkly funny.
On the negative side: The doomsday prepper who brought the useless hippie boyfriend into his bunker/compound. There is no way that I wouldn't have put the hippie on the road from the very beginning. That scenario was more than a little thin in the believability department in several areas. Especially the way that it was ended.