Only Kathryn Bigelow could take something as terrifying as the prospect of nuclear war and reduce it to a pretentious clichรฉ.
I'll save you two hours of your life: There is no definitive ending. It just stops, leaving you wondering what the hell was the point of any of that.
Bitterly disappointing, as this movie had a lot of potential. The way it ratchets up tension in the first 30 minutes is masterful. Then, however, it just repeats the same story over and over again from different perspectives, without offering anything new or interesting. All of the characters feel half-baked. The actors were clearly phoning it in; half of them didn't even consistently keep up American accents, frequently slipping into British or Irish.
For those who value substance, I'll save you another step: this is a poor screenplay adaptation of the superb book Nuclear War: A Scenario by Annie Jacobsen. I highly recommend Jacobsen's book for anyone who genuinely wants to take a hard, unflinching look at how horrifying this scenario would be. Unlike Bigelow, Jacobsen doesn't shy away from the hard stuff.