Helen Mirren and Stanley Baker (and to a somewhat lesser extent, the actor who plays Alsemero) really know what they're doing. It is fascinating to watch Beatrice-Joanna struggle with her lust for de Flores.
My sad little confession is that I suspect it is the lack of continuous score makes it a little difficult to feel the tragedy of the piece. Piraquo dies and I barely twitch, Diaphanta dies and the same. There's somehow a little bit of a wall between the audience and the evil.
In many of the smaller roles, the lines are recited rather than acted and this detracts from the meaning for those people to whom Jacobean language is less than clear. I watched it with subtitles and cannot count how many times the meaning of lines was obscured by mechanical delivery. Beatrice-Joanna's father seemed to be the worst offender to me.