So, yes I did watch the original.
If it makes any sense, I found the original really interesting and fascinating because it was Danish. Like the storytelling style is so different from English, Canadian, or US, some of the fascination with the original is that (in retrospect).
The lead actress in the original is really great. Just a solid actress with muted acting style that I liked.
It is 20 episodes I think, so the red herrings that are in the U.S. series are ever present in the original. It got really bad because I was yelling at the screen at one point: WTF, there have to be more than 2 cops who can investigate this murder!
now for the spoilers:
The original perp is not the perp in the U.S. In fact, the way Rosie was murdered in the U.S. was not at all the way she was murdered in the original. The character who died, the father's best friend is the perp in the original. And the final scenes in the mini-series were wild in how the perp was identified and then killed by "Rosie's" father. It was established that he had a lot of rage issues that couldn't be controlled, so the friend confessed to him in a situation where he knew he would be killed by the father's bare hands. And that's exactly what happened. While there were a lot of red herrings, the series really did a nice job laying the groundwork for the perp and how the final scenes were going to go down.
What I liked about the original is how much disdain the writers seemed to have for civic institutions. Everyone was corrupt: politicians, police. And their corruption was present throughout the investigation in ways large and small. The end of the mini-series is so dark tonally. Almost without a lot of hope.
I am in the middle of the second season, but I haven't been able to catch a minute to watch it with my full attention. The second is better than the first. Far fewer red herrings.