I initially scored this as an 8 because as far as I could remember, it was really good. But then when I re-watched this, I realized BSD's first season didn't really start off as a bang. I get that they introduce the characters with their abilities an/or story with each episode, which really did paid off for season 2 and 3 as well as the movie.
But season 1 was lacking something. It seems like they were just running around in circles with the 12 episodes and then it started picking up in the last moments. Another problem was having too many good characters. Let's be honest, they really did have promising characters with a cool premise of a detective agency vs port mafia; however, with the number of characters in the story, it's hard to be attached to them all in just 12 episodes, with no clear plot at all.
Thus, I gave it a 6 for this season only. However, one must not lose hope. For better watching experience, I suggest you continue watching till it finish because it'll get much better in the next episodes.