I sincerely liked the drama because of the main leads who did their jobs brilliantly well. The main guy had an aim to achieve but as he worked with his colleagues, they slowly grew on him and became like family. The one thing I specifically like about the drama is that they did not force any romantic scenes and that was good enough. Some KDramas force romance where it is not necessary, but Chief Kim stuck with the plot and was well done.
The character development was also really good as the series went on you could see that the writer factored in each person's role well. It also has bits of bromance here and there which I really liked. I would highly recommend this series, if you are looking for a balance between seriousness and quirkiness.