I'm 6 episodes into The Staircase and it's very good viewing for Staircase aficionados. It totally skips over much of the courtroom drama that was already well covered in the documentary, it's more a series drama about the drama in making the documentary. It has the feel of the French Lieutenants Woman, one love drama being played out in real time with another related drama from the past in the background.
I don't know how it would look to a person who hasn't already watched the documentary.