The acting is superb. Cush Jumbo and David Tennant bring nuance to their performances. The cinematography is smartly unnerving. The story itself was horrific and I felt the macabre sorrow it tried to repeatedly elicit from viewers, flashbacks showing us normal happy play from three beautiful children, climaxing with a full account of their deaths in the final episode (not a spoiler, we see them die early on) utterly gut churning in a way that was not entertaining whatsoever. It simply left me feeling rancid, temporarily robbed of my faith in humanity and vaguely alarmed.
Although argument can be made to say women and girls do die at the hands of male abusers, this is an extreme story to tell. It's not a true story and as fiction it's nothing more than a prime time gawp at the nastiest possible outcome of abuse. This is abuse as a spectacle.
In that respect I rate lowly simply because I found the subject matter insensitively handled. Domestic abuse isn't entertaining. To showcase it for nothing more than intrigue, with no lessons on the table for learning, seems distasteful.
Other reviewers mentioned plot holes, I agree, there were some key ones. The whole sad story was dragged out to keep us wondering if a twist would come into play and the effect was mawkish.
Off the mark and a missed opportunity.