'What's Wrong with Secretary Kim' is definitely the kind of drama you don't watch if you're looking for a fulfilling plot/story with proper suspense and climax. Instead, I found this drama to be highly relaxing -- I never once felt bored with the drama. Just as you start thinking that the story is becoming to serious/cringey/whatever, it switches over to talk about the other characters. The characters don't get very far in terms of character development -- the drama itself is a very simple rom-com, but I ended up falling in love with the main leads, as well as all the side characters! (Though, the older brother was a bit of a miscast, in my opinion -- it was probably the only time I felt un-engaged while watching) After finishing this drama, I get the same feeling I do when I finish reading something like a fairy tale -- things happen, things get solved, and they live happily ever after!
Rather than watching this for plot/character development/etc, I would suggest watching this with just a light heart -- enjoy the comedic and lovely moments between the characters, laugh at how extremely cringey some of the lines are, enjoy the great acting that Park Seo Joon and Park Min Young put on, look at all the pretty clothes PMY wears, and just smile!
