Have viewed most but not all of the documentary so take this with a grain of salt.
The way they were able to correctly portray the horrors of the period as well as the horrors committed by Ivan the Terrible was admirable. It's engaging as it keeps you guessing about John.
The complaint is when considering such a monstrous portion of history that is still relevant today, it's better that documentaries don't have the leisure of any heavy biases. I felt that even in the first few minutes the documentary had already decided a stance so I was extremely reluctant to continue. With the facts of the case so contested and the fact that there's a very real possibility that this man was Ivan the Terrible- a horrific murderer - it's better to be more objective. Objective was not the impression when the documentary started with the commentary from his close family, people who knew him, and later his attorney. The substance of the evidence was not explored but more so the conspiracy of a Soviet plot.