The episodes are not dragging. The solutions, inside the "universe" of the plot, are logical. The acting is believable. The cooperation between the main actors and the guests actors is good. The problems and life issues are believable. The CGI is good enough. It's funny enough, but also serious, suspensful and some times it's scary (in a mild way). It deals with serious social issues but at the same time it is written in a lighthearted way.
The story background (personal problems, mourning, romances, job etc) is important but it doesn't overshadow the premise of the drama. The heroes have a life, but they don't waste three episodes thinking about it. The episodes revolve around the stories and around character building.