I started watching this as soon as it was released and actually stopped in the middle of episode 1 as I felt there were a whole host of characters and they were introduced all at once. It was a bit hard to keep up with it. So I DROPPED IT!!! But there was that one weekend, I had some time and nothing good to watch..so I decided to give it a go. The series had finished airing by then and OMG am I glad I gave it a second chance. I binge watched the whole thing in 2days and 1 night. Here are some of my reasons:
Cinematography - So many beautiful scenes in this show. This is some quality program. You can really see that powers beyond the actors took time to stitch the story well. Simply amazing.
Costume - I watch a lot of Sageuks. But this one takes the cake for costumes. It might be because there are a lot of female characters in it, but the hanboks in this drama deserve their own series I think.
Acting - Top notch acting all around Period!
Story - Going into it I was not convinced that story of palace "back office" would be that interesting. This was proven wrong by episode 2. You really do not need heavy romance, always conspiring Left/Right state ministers for a really good Saguek.
Restraint - We often do not value restraint that much. Most stories do not exercise it and while they all make decent watch, they do not make for memorable, impactful pieces. I loved how the storyline had so much restraint. It was classy all around.
Romance - There was very little of it. However it felt really relevant to the story. They did not overdo it which made the romance itself very enjoyable
Characters - The story had such strong characters. If you have young adults in your family, I highly recommend watching it with them. There are a lot of life lessons here that they would enjoy.

I could go on. All in all, this is one of the most memorable dramas I have watched in a long while. We need more of this!