True crime documentaries take the perspective of either the victim/family/community, the perpetrator, or the investigators. This is a quality entry in the last category. Given that investigation-focused content is less frequently produced than the other types, it is a welcome addition. People who seek out the first perspective should be warned that there is little here for them.
The second season improves on the first and has the benefit of compelling and atmospheric cinematography and very good production values.
Viewer engagement requires overlooking the somewhat contrived convention of discussions (many one-sided phone calls that are fairly obviously staged for the camera man) between the criminal psychologist David Wilson, and the experienced true-crime presenter (and actress, but she's getting quite good at non-dramatic presentation work) Emilia Fox. This is basically the only non-dramatic way to communicate investigative avenues and activity.
I will not speak for the family members of victims but in terms of the justice value, the show does fill the gap that exists in cases where trials will never be held and the likely perpetrator is dead, and that is a meaningful community service. They cannot succeed in this with every episode because this is about real life. The show also gives a very realistic depiction of challenges experienced by the police without flinching when confronted with probable police incompetence (and a couple of instances where the police themselves admitted failures under subsequent review).
In a nutshell this is a show for people who like watching true crime documentaries that take the perspective of police, criminologists, forensic scientists and other experts, rather than family and community members, or perpetrators. It does not indulge in gratuitous, immature or salacious punditry. For drama-watchers, this is for people who liked Unforgotten despite Nicola Walker's hyper-emotional portrayal of DCI Cassie Stuart and not because of it.