Not a robot, a human/machine composite. All Sec Units are self-aware, as are many of the actual robots in the series, but only Murderbot has free will. One of the themes of the book series is the burden and anxiety of suddenly gaining free will, so missing that is kind of missing a major point of the Murderbot series.
The season was very good, but they couldn't communicate how alien the sec unit's mind was in the books, observing the human condition from outside.
I have been a fan of Murderbot since Martha's first book. All the new stories, short and long download when they come out. Kind of ironic to have AI narration.