Simplest way to say it is that they both a rich men/man and a poor woman. Their lives are changed by eachothers impact!

Both have the same actress and emphasize the female lead feeling at loss because of their age. They both struggle to find what their own place in society as well as from misfortune in love.

Rich Men and a poor women. One talks more about the fancy lifestyles about the rich than the other but both main leads are peculiar and have interesting personalities. The second lead tends to have some air of mystery, but are good guys in the end. Second female lead in rich man poor woman is similar to one of the girls that become interested in Jun Pyo as well.

The story of childhood friends who are in love with eachother, and of course the third parties that they meet along the way (love triangles! or squares?)
Both have a similar air, where they are not that extremely dramatic or serious but are light hearted in a sense.

Somehow the dynamic between the couple reminded me of this drama. Problems between a married couple, though one of them additionally features a child.

Same idea of trying to help a class of troublesome students, a life-changing school experience, array of characters and so on. Strongly recommend.

Same idea of a class of troublesome students, and an optimistic person (in gokusen a teacher, and asuko march the only female student) who help turn everyone's lives around. Scheme of the episodes it similar, that it goes through various characters and shows the efforts of protagonist and their kind hearts that bring resolution to the issue.

Both historical dramas that are 50 episodes, and take place during the same time period of Gwanghae's life.
Each are a different story of what goes on, but they have similar characters.

Another historical drama about the corruption of power. Also, they are both about the strength of the people, good over bad, and the struggle for justice.
I find that even though the plot lines may be different, one being about a princess and one about a vampire, they have very similar characters and character relationships.

The female lead in both dresses up as a male, for their survival, in the early part of the drama. They are both bright and friendly, though, Jo Yang Sun isn't as thoughtful and clever as Jeong Myeong. Both have a strong fate with the inner workings of the palace.
Both male leads are kind and caring, and will go to the lengths to protect their leading ladies. Their caring love is what makes you heart race while watching the drama. Difference though, Kim Sung Yeol is a vampire and Hong Joo Won is a bashful scholar (well he moves up in rank through out the drama) .

The royals in the drama are similar too, where, as much as they want to fight the corruption, its extremely difficult. In the process, they lose their original goal and stray. Their mission throughout is continuously remind themselves of purpose and try to find the right retainers.

They both have a similar comedic feel while the main basis of the plot being on the romance itself. Similarly, you can find both have an interesting love triangle relationships.

It has a similar shoujo, light and fluffy vibe to it. In a way, the female lead has a similar charm to her, and they're but pretty cute. The main male leads are both tsundere as well, and they end up becoming increasingly kind of the female lead. Both works are by the same director too!