Yes, I loved Series 1. But then series 2 was all "gruesome fascination" as you say.
I haven't read other posts yet (will do) but though the final episode was weak in many ways I kinda liked the ending. It was almost calm by comparison to previous two episodes, and tied up the loose ends, emotional and physical (with them all going their separate ways).
I like that no-one died!
I like that the son escaped from his two parents.
The father was shown as still an unpleasant and selfish character Though there was mentioned of a mother he "looked after" and a father "he hated. Regardless, he was still the psycho.
I think a bit more space was given to the mother. Its like she lost her parents and then lost her husband (and nearly her job, her house, her money too) and she held on to her son - too hard. In the end it was clear she was holding on to him as much for her benefit as his. And I remembered how she abandoned and embarrassed son at the husband's wedding party to snoop.
It was a bit of a shambolic ending, and mostly unbelievable.
But it was realistic somehow in that there was some resolution.