I don't like slow drama but this set a great pace to build the story to the ending.
Acting was superb by almost all the actors. I have never felt so much emotions while watching a drama. It made everyone feel patriotic, even the timid ones.
Cinematography was astounding
The way the story unveiled helps the audience keep track of a character's growth.
The writing was beautiful as well and totally suits the period, including the fact that the main character never kiss at all
It's a rare shows which has many different languages spoken by so many actors perfectly. Even non speakers can tell the difference when the Korean speaks Japanese and when the Japanese speaks Korean or English. That's how great the acting was by every actors and actresses.