I caught up with the last episode last night. I agree, superbly well acted, but a little rushed. What really chilled me was the way Christie acted after the murders - looking almost bored as a pp said, and a kind of world-weary 'oh well, now I suppose I've got to do something with the bodies, it's a nuisance but it has to be done'. And for some reason, him leaving the dog in the park got to me as well, even though it was completely insignificant in the scheme of the other terrible things he'd done.
On Ethel not leaving him, there's a book by Michelle Magorian whose title escapes me at the moment, also set in the bleak post-war period in a working-class community, which has a woman in it who's presumed to be divorced - she's shunned by everyone, and her son is victimised in school and no-one's allowed to make friends with him. I think the acceptability of divorce (or separation, or abandonment) in the 40s and early 50s, and the viability of your life as a no-longer-married woman, depended a lot on where and how you lived, so I can see why it wasn't an attractive option for Ethel. Additionally, she would have internalised the beliefs of the time about it being a woman's fault if her man strayed etc. (If you ever really watch the musical Carousel it's quite shocking in its portrayal of casual domestic violence, but it was completely unremarkable for its time.) Poor Ethel, though. What a life - and death.
I first knew about the case from by Ewan McColl.