This drama manages to earn the name "drama", there's a lot of dramatic tension in this. I enjoyed the way the show mixed elements of a fairytale romance, military war games, political power struggles, arms dealers and the actual threat of an outright war. This expert mingling of plot lines kept the show very entertaining as there was never a shortage of storyline. The love story is well developed as the two leads are a couple for the majority of the drama, their angst and separations always had a political cause not personal, this was a shift from the usual plot devices in romantic dramas. I didn't detect any noble idiocy in this drama, the two leads thought out every problem and made well informed decisions.

SPOILER ALERT: What I particularly didn't like about the plot was the killing of Eun shi gyeong, was it necessary to kill him? I found his death particularly annoying because it didn't actually result in the definitive capture of the villain, his death felt pointless and a waste of a good character especially after show developed a love line with shi gyeong and the princess, had this romance been fully realised, it would have nicely rounded off the bromance between the king and shi gyeong; this bromance was so well depicted only to have it cut short with his death. END SPOILER

Overall this drama is about the making of a good king and this story was well told. Lee Jae Ha started off as a bratty, irresponsible, playboy prince, and ended up a strong, resolute and mature king, I liked that he retained his sense of fun to the end.

The casting and acting was spot on (except for the foreign English speaking actors, these were horrendous and had too many lines in my opinion ), there were no weak links in the central cast. I absolutely disliked Ha Ji Won in Secret Garden (to the point that I vowed never to watch her again), but I loved her in this role, she embodied Kim Hang Ah's badass toughness and soft femininity perfectly.
This was my first time watching Lee Seung Gi, he was very good and damn near stole the show, but not quite in my opinion because of Ha Ji Won, Jo Jung Suk, the queen dowager and Hang Ah's dad. The acting is superb in this drama.

The music is ok, I liked the ballad but was not a fan of the dramatic orchestral music as I found it a bit overdramatic; the story was engaging enough to not focus on the music.
The cinematography is fantastic though, this is one beautifully shot drama.

I'm not a great rewatches, but I'll give this an 8 rewatch value, I've rarely seen a drama as polished as this one.

My overall score is 9.5