Sageuk Lover

King Sejo/Suyang didn't become just a "nice" person in the end of the drama. The last few episodes of the drama shows him being guilty by his conscience, his skin disease, some haunted dreams of the people he killed. For all his wickedness, we see in the show that the evil king did love his family. I think both his son's death and seeing his beloved daughter happy with a new family (and the fact that he was getting old) made him change a bit. The writers couldn't just kill him because the historical king didn't die. Some recent kdramas tried to change historical events and they got cancelled.
You have to also take note that the female lead is pregnant. Most other people on Kim Seung Yoo's side are dead as well. Kim Seung Yoo became blind too. Those details contribute to the factor on why Kim Seung Yoo stopped his revenge and why the ending is that way. And I don't think the ending is rushed or just decided on the spot because the ending is indeed the ending of the legend/years long rumored romance between an alleged daughter of King Sejo/Suyang and the chilf of Kim Jong Seo.
What this drama did was to fill up the blanks missing from the historical events as well as what is known from the legend of the romance between Suyang's alleged daughter and Kim Seung Yoo's son to create a compelling romance.

Okay, okay. I'm not denying the fact that the female lead in the drama you watched really suffered a lot. But that doesn't erase the fact that the female lead here suffered a lot too. Emotional suffering shouldn't be taken lightly anyway. Plus none of Seryung's family members tried to understand her which made her guilt feel bigger since her own family members feel heartless towards the man she loves as well as doing the right thing (none of her family was against her father banishing the former teen boy king). Emotional suffering only? Her father disowned her, made her a slave to a man she does not want to marry. Those are really painful sufferings since almost all her life this was the father that doted on her.
We were just talking how much we love this show and I'm really sorry if I really love this show and personally feel you're quite trying to put it down (what with your negative comments about the ending as well). Really sorry

it's supposed to be TPM, meant for The Princess's Man

she's a great character because she's a character who grows and develop throughout the drama. she's young and naive at first. but she did owe up to her actions, even risking her life to save the male lead (even after male lead tried to kill her father).

her father told her not to tell him. plus she did not know how dreadful would be the result of the male lead not knowing who she actually is until it is too late (if you remember, she only accidentally heard her father's plan to kill male lead's family).

try The Red Sleeve

all sageuks used to be like this. the use of teeny bopper songs with english lyrics started only with the youth oriented sageuks,.

the first king is weak and sickly and his only heir is a teenage boy. he has a very ambitious brother. so naturally the brother will use this opportunity (his brother's sickness and his brother's heir being young) to get his ambitions. the weak king did have a strong supporter (general kim jong seo) at first which the ambitious king was very successful in fooling.

For those not liking the ending, please watch these videos:
https://www.youtube.com/watch?v=ue_lxcEWioU
https://www.youtube.com/watch?feature=shared&fbclid=IwAR0qlPRHmlnYaSOuZB6m7DKZ8TzoXLkwM4_s_eywPOz9bS_HHmDw3h3B31w&v=cwnD1nd9iN0
=> both are in Korean but you can check the comments in the first video for explanation of the summary of both videos . First video is actually a documentary that discusses the historicity of the lead characters while the drama was being shown in Korea.

This is not 100% true of course but the link I posted are about Koreans debating the existence of the titular princess in the story. There is really a rumor that the king really had a princess that ran away with her lover (son of her father's enemy) and that years later the princess's father met his grandchild through the princess, which is a similar ending to the drama. Here (https://www.youtube.com/watch?feature=shared&fbclid=IwAR0qlPRHmlnYaSOuZB6m7DKZ8TzoXLkwM4_s_eywPOz9bS_HHmDw3h3B31w&v=cwnD1nd9iN0) shows this very similar story based on the rumor (video is different from the one I posted above). Notice how both this video and the drama had the king seeing his grandchild years after the princess ran away from him. This drama is partly based on this rumor and they followed this ending (princess and lover living in hiding with king seeing his granddaughter years later) quite faithfully.

I think Seryung's status as a princess is part of why her suffering is great since the cause of her suffering (her separation and all the troubles of her lover Kim Seung Yoo) is all caused by the father whom she loves who happens to be super ambitious and desires to be king.

What's the title of the sad song sung by a man which was sung when Jang Hyun throw shoes in the water? It's a beautiful song.

A very good show! Namgoong Min and Ahn Eun Jin are amazing.

Flower of Evil should not be here, the female lead (a very talented actress) is not recognized enough for her role and contribution for the drama.

It's not my top sageuk, but Mr. Sunshine is certainly a drama that doesn't deserve a position here.

There are many good dramas (particularly older historical dramas, when I mean older, a historical drama that aired prior to 2012) that aren't seen by people.

Dramas like Descendants of the Sun and Moon Lovers Scarlet Heart Ryeo (I consider overrated among sageuks) are two overrated dramas that I didn't vote because I believe the charm of the male leads' are good enough to save these two shows.

She's so gorgeous. I love her

not necessarily it's just that the second lead actors are my biases and it's so hard to not root for them. when i first watched this in 2009 i was fresh off my fangirling for a sageuk drama (aired 2008) both second leads appear in. i think you'd feel the same with sjk. the sfl also have no malice at first when she loved the second male lead plus second male lead is also genuinely nice to the female lead. doesn't help that the second male lead and female lead reunited in a drama (Dong Yi) a year after this having the same kind of relationship.

Time Between Dog and Wolf (2007) and Shark (2013), both revenge based dramas that have dramatic soundtracks.