The movie has three chapters. Each chapter is the 18 minutes from the time the nuclear missile is detected over the Pacific until seconds before the assumed detonation above Chicago. Assumed detonation? Yeap. The Netflix PR page describes it this way. "For Bigelow, the film's unresolved ending is an invitation."
I watched what I later learned was the first chapter. Seconds before the assumed detonation the screen went black. Minus the end credits - there were ~65 minutes left. Where could the story go? I knew nothing of the structure of plot and the three chapters but I knew in my bones that there would be a 99% chance I'd hate it.
What happens in chapters two and three? I have no idea. After the screen went black. Chapter two started with a shot of a single Civil War reenactor in the woods. He twirled his revolver. What the fucking fuck. I watched another ~3 minutes of chapter two and then paused the movie. I googled and I checked Wikipedia. I learned of the movie's dog shit structure. I didn't watch any more.
In chapter one it's strongly suggested that everybody is certain the missile is about to kill at least 10 million people after it hits Chicago. And there's massive panic at the White House. A low-level guy functions as a plot device. He asks an elite natsec guy the question "Where's everybody going?" The elite guy answers by saying "They're going home." This obviously implies Washington will be destroyed.
I like ambiguity. What I don't like is being led down the garden path for 60+ minutes to a tedious and very annoying non-ending.