I'd like to say that half of my kdrama (and also some jdrama) experience is the music, the soundtracks from the series I watch. I have them on my spotify list when I go out for a walk or jog, and it's all I listen to, also at work, and at home I blast them.

They enable me to enjoy series even long after I've watched them. Just hearing the soundtracks brings the series to life in my mind, almost flashing before my eyes, while enjoying great music.

Sometimes I've enjoyed soundtracks from dramas I haven't watched yet and decided to watch because of it.

Music is good :)

agreed, the music makes the dramas more memorable for me - not just the OSTs but the background score too which I also find important in a drama besides plot/characters, it adds to the overall vibe of the drama. I made a thread about the BGMs before, feel free to post some of your favourites there if you want. 

What about music played in dramas by characters?  I recently watched cdrama First Romance, where ML is a pianist and some pieces where incredible..

Short example (possible spoiler): video