This drama was, overall, a disappointment. There were huge plot holes and stuff that didn't make sense and went against logic. The character Oh Maria was terrible. Lee Joon was excellent and Yoon Sang Hyun did very well with what he was given to work with. (But then I'm biased, YSH is one of my favorite actors). This could have been a very good drama. I blame the writers.
"Take Care Of The Young Lady" made a dedicated Yoon Sang Hyun" fan out of me. I initially watched it for Jung Il Woo. Also, TCoTYL was made in 2009. The age difference would still be the same but Sang Hyun was not yet 40. He turned 40 in 2012 by Korean standards, 2013 by western calculation.