Recommendations

Both are the same story of the same person with legend narrating the story with fantasy elements. The story focus on Damdeok later, Gwanggaeto the Great. Although the story is entirely different legend is watchable once.

Both movies have a similar comedic style. Slight slapstick and fun jokes. Overall both are very fun movies that you can enjoy

They both start with an explosion and have a little comedy, the story also include gangs and violence , both have good acting.

Both show a relationship that blossoms from friendship and what happens to that relationship when tough times hit. The leads in both have great chemistry and you see characters in most struggle to “make it” in the workplace. The family drama in Us and Them is more poignant

Both historical dramas were about the story of a King (Different Era). How he made it to the top and how HE had to kill a brother before ascending to the throne and how he lost his loved one in order to keep the power. Both tackles about Family issues, Inheritance, Power struggle, Forbidden Love, and Delivers the right amount of Bromance.

Both have Kwon Sang woo as the lead except his role is reversed in both dramas. In
QoM he is detective where in TAD he is civilian who has interest in solving crimes and helps the detective. In QoM the civilian role is done by Choi Kang hee.

Both shows give insights into the private lives of famous people. The comedy and life lessons shared are what make both shows hits!

As you can see from the title, both these dramas deal with Empress Dugu. However- LEGEND of DUGU revolves more around the lives of all 3 sisters and how their story intertwines.
Meanwhile, judging from the plot of Queen Dugu, I'd say it will be focusing more on our main girl and her counterpart and their love story.

While watching "Gekiryu~Watashi wo Oboete Imasuka?", I felt the same bittersweet feeling with "Piece". The plot is similar: former friends from high school try to resolve an accident which occurred many years ago. Step by step, layers are shown, prejudices and lies are revealed. During this journey, they will question themselves about the meaning of their present lives and learn about each other. "Piece" has more mystery, "Gekiryu~Watashi wo Oboete Imasuka?" is more focused on the people’s lives.

Both have:
-older/strong/unfashionable female lead
-hate/love relationship
-similar humour/comic relief scenes
-rival girl is both pretty & lowkey has issues
-"man candy" character (Daniel Henney..<3)
[note: there might be a slight age gap]

Main characters met once during childhood/younger age, specifically during some kind of traumatic event.
They meet again many years later~

(Male leads from both dramas have similar personalities too)

I have not watched How Long Will I Love U but It sounds like the Meet Me @ 1006 and How Long Will I Love You have the same concepts of time travel. With merging of apartments, going in and out of certain doors leads to different time periods, etc.

Both dramas follow the main couples love through many lives.
The male lead in both shows are in a position where they hold a lot of power. and the female doesn't remember her past with the male lead.
All in all both dramas are similar in a way, but i wouldn't say they have a similar story line. it's definitely different.

A love story between the boss and the secretary. Unlike the common chaebol parents, the parents in both drama are very nice and love the female lead. Both dramas are very funny. The chemistry is also great.

In both stories, the guy already has a son and struggles when he falls in love with a new woman. However, this is a more serious take on the situation.