I believe that the most natural sounds of our surroundings are the best bgm for scenes, and when I watched this drama, it wasn't just different from others it was also soothing to my ears. Nowadays its just useless music for every scene right from happy scenes to sad scenes , even when someone walks there's music.
The most natural emotions are not those which are over done by actors ,instead the ones which are most subtle and believable are .If I had to suggest this drama to someone I'd do that to someone who's bored of watching k-dramas with the same plot and characters and even the way the scenes are shot, if you think you can't complete any recent drama that you have started watching or are watching them just to end them ,then you should take a break and watch this drama instead.
Just the fact that the use of bgm is so less makes it so awesome ,but also at end of the drama you might find them using bgm ,but I promise its not overly used ,its used only when it was needed the most.