They are bright and colorful
When the use of HD cameras started in 2010, Korean pictures became significantly clear, vivid and eye catching. That was one of the things that made Korean cinema very popular in the past few years.
K drama is a good teaching medium
Korean dramas endorse family values and are a good teaching medium for preteens and children. They’re also relevant for family viewers, as there is nothing sordid or gritty in them.
Some of them have happy endings
Audience always long to see the heroine reaching her goal in the story. Korean movies usually make the heroine/hero emerges triumphant at the end not matter what troubles they go through.
The settings are attractive
Audiences always like to see luxury in movies, and K dramas are capable of providing such richness in location through hi-tech private homes, outstanding outdoor views and luxurious outdoor settings.
The acting is good
Korean actors and actresses are very attractive, and they’re also very good at doing their jobs. Korean directors always pick the most attractive actors, based on their awareness of what the audience want to see in them.
They have good costume designs
The clothes worn by Korean actors are usually very stylish and well designed. Koreans are known for having a sense of style, and even average Korean people are always well dressed. (See Why Netflix is so popular?)
The have good storylines
Story-lines are always well-thought of in Korean dramas. One other thing that makes the stories very interesting also is that Korean actors are always in character.
They make good soap operas
TV shows usually range from 16-50 minutes to an hour each episode. No matter how the writers try to stretch the plot to fit the length of the whole series, they try to make it look more interesting than other soap-operas.
They discuss family issues
K dramas always build stories that are about family issues like the relationship between mothers-in-law and daughters-in-law, fathers and sons, mothers and daughters, and between siblings, but in the end all the problems are resolved.
Usually K dramas splash scenes all over the story where characters start expressing their feeling to each other. Korean dramas also interestingly reveal very homey scenes, like a group of people dining, for instance.
K dramas mastered cliff-hangers
Korean dramas are very good at teasing the audience to keep them wanting more after each episode. (See Why do people binge-watch TV shows?)
The protagonist is usually a woman
K dramas have a wide range of women audience, considering the great emphasis on sentiment and family issues. Base on this, it makes total sense that screenwriters usually pick women as protagonists for their stories.
The Mountain And The Viper - Game of Thrones Season 4 Episode 8 (Summary)