Now ten years old, this documentary spans Argento's career, from his film critic days right up to some of his latest work. Unlike Soavi's documentary, which focused on "Phenomena" and a few Argento interviews, this is far more of a complete biography. (Both films are good, but the focus is different.)
Here we learn that Argento hates actors, and prefers the look of a scene over performances. He also does not like directing because he prefers to be alone. Being surrounded by people asking him questions annoys him.
The documentary asks, but never fully answers, what might be a psychological question: why he killed his wife Daria several times, but never killed his daughter Asia -- only raped her and has her naked in multiple films. The answer is potentially disturbing and best not to explore.
Overall, this documentary is very in-depth, extensive, informative and has such varied interviews, notably from people early in his career, or modern masters of horror like John Carpenter or George A. Romero.