Although different in plot, these are both comedies that feature Matsuda Shota. If you liked his wacky and very funny character in Don Quixote you might be interested to watch more. He has a quirky character and great comedic timing in this drama as well.
Both feature not only a hilariously confused and wacky lead male character, they both also feature a fairly strong, sweet lead female and a charming and winning second lead male! They are both smartly written with tender moments and a ton of laughs.
Although The Princess' Man is more serious and intense, Hong Gil Dong also features a really great love story in the plot. They are both Sauguk/Historical dramas where the action speeds up as the episodes progress and both very well written.
Both are Sauguk/Historical dramas that star Jang Hyuk. Although different in plot, they are alike in that they are both very well written and excellently acted. Each are 24 episodes and a ton of fun to watch!
Both of these dramas have a lead character who falls in love and it turns their narrow world upside down. It also makes for great comedy to watch the confused and wholly selfish chaebol become a huge, hilarious mess and eventually a better person for the person they love.
They are both Joseon-centric Historical dramas with emotionally and mentally strong, intelligent female characters as the leads. They also both contain similar values and have overlapping cast in places. (Dong Yi takes place before Dae Jang Geum...)