I thought that the first episode was a bit slow and had too many plot holes although, as I am not going to write "spoilers", I won't list these. But they did reduce my final rating from 9 ot 8.
However, having now watched all the remaining 5 episodes, it does get better as it goes along - with fewer plot holes - and finishes with a good last episode, with no open ending laying the ground for another series.
I thought that all the actors playing the main characters did well, and there were few weaknesses. I also liked the writing and direction and, unlike so many crime series these days, didn't rely any chases between the "goodies and baddies" to bolster the plot.
This series is well worth four hours of your time.