The good bits - I like the acting and the characters are largely sympathetic. Broadly the stories are good. The photography conveys the bleakness of a cold and dark of a nordic winter.
The not so good bits.
1 Appalling editing and continuity. Snowy landscapes in Finland one minute, snow-free landscapes the next in the same places and the same supposed timeline. In series 2 Helsinki is blanketed with a deep layer of snow, whereas Tallin (about 50 miles south) has nothing at all, not even a hint, doesn't even look that cold.
2. Ludicrous plot holes. Again in season 2, someone has just tried and failed to kill the Mayor at her office. The police know this is part of an ongoing series of murders yet they drop her off at her home without leaving any kind of police presence at all. It's as if she's just come home from a night out. Then in episode 7 our two protagonists find a helicopter in a derelict prison which. amazingly, has full and can fly even though it's just been sitting there from some time. And Nurmi can fly it, although he's not a pilot. Stretching things a bit too much.
I'm still gonna watch the next episode, though, just to find out if they survived the flight in a rickety old helicopter piloted by someone who's never flown anything in his life before!