This was a notably disappointing movie. Errol Morris thought he could make another The Fog of War and instead he got hours of Donald Rumsfeld saying basically nothing.
It's hard to imagine what's in the many hours of footage Morris didn't use. The filmmaker has said that he knew more about the decision to invade Iraq before interviewing Rumsfeld than after, which strikes me as plausible. I had a review of a worthwhile book about Rumsfeld here.