@Czak
Again, I respectfully disagree. I saw lots of chemistry, just not the palpable kind we're used to seeing in romcoms of this nature. I thought the actors portrayed their characters well, esp the Sung Joon. In fact, I loved his character here.
You also have to remember that he was playing an ambitious man who wanted to excel in his career, but due to him not being born with a silver spoon in his mouth his journey was a lot harder and that made him a bit reserved and distant (esp from the FL who he perceived as a spoiled little rich girl who just had everything handed to her). When it mattered, he portrayed the appropriate emotions. As for UEE I thought she did fine, I really do. I haven't seen Marriage Contract, but to me High Society was one of her better roles (I've seen her in other stuff and I was mostly just indifferent to her, but in HS I liked her character and how she portrayed her).
The issue I had with the drama was not so much the characters or the actors, but the writing itself. They proposed a few fresh ideas, esp when it comes to the relationship between adult children & their parents, but never really went through with them, which was a disappointment. When it comes to the characters, I was satisfied, and I think that's why one's enjoyment of this drama and this couple will come down to a number of things - taste, life experience, what kind of romantic relationship you enjoy etc. I certainly liked the 2nd couple, but for me they came no where close to the leads.