Great King Sejong was the drama that helped me to get out of drama slump after I've watched NiF.
It has many similarities to NiF, the prince is underdog and has ppl who help him to become king and beyond, in a way it is NiF story told from the perspective of the prince (without the revenge part). It is however a much longer and slower drama with a lot of talking.
Another drama in similar vein is Six Flying Dragons, it is absolutely well put together and a must watch for anyone who likes historical fiction, I think