If you like a documentary that presents unbiased facts, this isn't for you. The narrator sensationalizes quite a bit, throwing around terms like "the most evil" frequently. There are only a couple of "experts", who are just some folks trying to sell their books for the most part. These are not legal or psychological experts. Often, just people who have done a few interviews with a few killers.
In the very first episode they tell us that we're totally wrong about most serial killers being white, and then will up most of seven episodes talking about white serial killers. By the end it's really just "more of the same".
What I did like is that it gave attention to less known cases. Nothing beyond that brings anything new to light. It is a well produced show, though.