I binged-watched this in one evening mostly because I was afraid that if I stopped I would never go back and finish it. I gather that happened to others. But I had the time and in the end it was a great ride. The story moves from one theory to another about one man's death over the decades--and the final conclusion is that his murder can't be solved unless a whole lot of other ones are brought to light at the same time, as well as some very dark moments in America's past. That is a worthy theme for 4 1/2 hours.
As the story moves on, you realize that the collages of news stories, photographs (e.g. of actual people mixed up or jigsawed into the actors who play them in the re-enactments) and places are deeply tied into the story: the main character, Eric Olson, began making collages after his father's death and later developed a method for using collages to help traumatized people deal with their experiences. It seems to me that this method fits well with Morris's style, and the rhythms of the images can be very beautiful.
Eric lost track of this work, apparently moved back into the house he lived in as a child, and talks at the end about having lost himself in his search for the truth about his father. He remains however extremely articulate and persuasive. In a sense, the film itself redeems Eric and his father by exposing the secrets they wanted known.
