I think one of the main issues is that Helen is a poor choice of main character. Helen's an icon but she is a bit of a pale imitation of Sarah Lund and I think, given the developments that happen in the second half of the season Camilla would have made a better main character as she has ties to the killer that would have given their storyline more gravitas if it was allowed to develop further. She's also a character that doesn't really occupy the same mould as Sarah Lund or Saga Norén which would have helped the series stand out more.

I think the relationship between the two gay characters is badly handled too, it feels a bit too typical and it gets pushed to the wayside early on until near the end of the season which gives me the impression that the creators were more concerned with making them the USP of the series rather than pulling off a good portrayal of a gay storyline. Another problem is that it's difficult to root for them because only one of them is likable and well developed. Philip's a great character but Henning is just a little bitch for most of the series until his character does a random u-turn which just felt convenient to the plot rather than a development of his character.

Finally my last big issue with the series is that, although it's only 6 episodes long, they could have dropped two episodes to make the story a bit more pacier. The middle section of the series feels like the characters are waiting around for the story to catch up.

That being said though, I did like it a lot. I thought it was mostly well acted and the Killer was interesting although he felt a bit underdeveloped, the advantage of knowing who the killer is from the outset should be that he is well developed by the end of the story but they wasted that opportunity somewhat.