I want to know why Ruth is so abrasive but without knowing she just comes across as rude.
I think they gave quite a bit of time to her background in her first series, and with the very stagey opening episode of this series gave her the time to speak a re-cap. (Including as now seems unavoidable a negative Shetland family experience!)
What I think is wrong is that the scenes between her and Tosh are now always the same. Ruth ready to dash in, Tosh ready to say lets think about it, what are the rules.
In their first series together they had some interesting conversations. I wonder if it is a different script writer this series.
And agree with comment by PP, Sandy is just and extra allowed a few lines.
And it would be great to have a case where there weren't always unpleasant knobheads (usually outsiders) in pretentious glass and concrete modern statements, and local families somehow locked into a daily drama of family tensions and old vendettas.
Why not a story about the nice couple who run the corner shop and then unruly tourists misbehave, and it all escalates, and in no time Shetlanders come together and launch a campaign to stop unpleasant outsiders ruining their island. Something that says more about living there than most episodes do. And yes I supppose it would have to have a few murders thrown in!