I watched it with DD (15). We both enjoyed it. She had said from the start it would be the son. I couldn't (didn't want to) believe that.
I, too, liked the fact that there was not really a twist. I have two teenage DSs. We discussed after the programme, briefly, what we parents would do. Asked the DC what we should do. I was very pleasantly surprised when the two that are at home atm both said that we parents should, of course, turn them in if they had committed such a crime (or really any crime).
It provoked a lot of thought in me while I was watching it. Would I be the same as Hermione and keep making excuses and believe the plausible stories that the son gave? He kept promising that he was telling the truth and his reasons for not telling the truth each time he was found out seemed very believable. I really searched my soul after watching it and found that I really didn't know what I would do, up until she really knew that he had done it. In that situation I know that I would immediately turn him in, but would I want to believe everything that he told me? In this house, if you absolutely say that you are telling the truth, then you are believed. That was what was difficult for Hermione, I think, the fact that he kept insisting that he absolutely had nothing to do with the girl's death.
I don't usually watch 2 or 3-part dramas, but I really enjoyed this one.