The series is about a homicide detective, the people around him and his mental state.
This series is very well executed, all questions get answers. There are even a few plot twists that I didn't see coming. The characters are believable, and they are acted skillfully. It captures the social conflicts in Turkey well. The murder cases are usually interesting. It is one of the best shows I've ever watched, a list that includes many expensive Hollywood productions. It was actually very surprising that I'd like a show from Turkey this much.
There are a few negative points however, for which people who consider watching this should prepare themselves. First, there is a lot of swearing. This is made worse by the censorship enforced by Turkish TV. All the swearing is bleeped out, so sometimes it feels like you are listening to a voice-over by R2D2. Some visual elements are censored as well, such as alcoholic drinks later in the show. As the last point, English subtitles are not very well translated. You'll get the point, but sometimes how something is said is important to capture the depth of the scene, which is typically lost.
All in all, I'd recommend this to anyone who are interested in a police drama.