These are not korean but very good still..
The Great Revival - I made a topic in the past looking for a chinese historical drama which had realistic characters since at that time all I could find were cheesy shows. It turned out to be a lot better than I expected and still one of my favorites.
Legend of Concubine Zhen Huan - Very good. Randomly watched an episode but ended up finishing the whole drama when at the time I had not finished a drama in months. The thing that hooked me was when in the first episode (I think) the girl who seems will be the main character's rival throughout the show is killed.
I also know some other older korean historical dramas / not as well known. Most are pretty hard to find but they are on aznv.tv (I think site needs an account to watch shows on though)
Ballad of suh dong - This was one of my first historical dramas. I think I watched it after jumong which was a long time ago.. I do not remember too much but I know I liked it.
Gu Am Heo Jun - A recent drama about a doctor.. I do not really like medical stuff so it did not interest me.
age of warriors - Only watched the first episode but the place I watched it from the quality was not so good + acting seemed bad. Not sure why I even mentioned it lol..
shin don - I liked it a lot but.. towards the end I dropped it.
immortal lee soo-shin - Like age of warriors quality was not so good and acting seemed bad. I also was not really interested in the guy even though hes one of the most famous guys in history.
Empress Chun Chu - Did not like the lead but I did watch a good amount still.
Emperor Wang Guhn - 200 episodes... and from 2000 when acting was bad + hard to find decent quality. Still though from the 20ish episodes I watched it seemed to be very good. This time period also is very interesting since there were so many different groups trying to start up their own kingdoms/empires. I always feel like one day I will definitely finish this but... 200 episodes without good quality :////
Dae Jo Yeong - From what I remember it seemed to have a different plot than most. A guy going from nothing to founding a nation. The problem with the show though is there was no place to stream it. I had to download each hardsubbed episode and my internet sucked so 134 episodes would take forever. I am also not sure where I was downloading the episodes from anymore.. but I also feel like I will finish this one some day.