I have to admit that I was expecting much more from this drama. I usually don't watch historical dramas, but I have heard so many good things about this one, and the fact that Park Hyung Sik was in it... I couldn't stop myself. 
 Story: the first 5 episodes made me been completely hooked... they were interesting, funny and I liked the story, the secrets, the enemies...
After that, from the 6 or 7 episode until de 12 or so, the story gets messy and it focus only on the love triangle (ok, let's be honest, there's no such thing as a love triangle, since the beginning one of them - if you have watched the show you know whom - had 0 opportunity). Half way I was more interested in a second love story that the main lead couple. Luckily, it gets again better from episode 13, more fighting, friending and intrigues until the end. 
Besides, in my opinion, there are too many dead ends in some things they have should explained better...
Acting/cast: I liked the male actors, overall Park Hyung Sik as the hidden King and the Hwarang second leads. On the other hand, I couldn't stand the female main lead. I usually don't like when women are extremely stupid. I know it depends on the time the story is set up, but anyway, Ah Ro was unbearable.  I agree with some reviews that say that the main female lead only knows how to cry, be saved and make silly faces as she is angry or mad at the main male lead. It's was tiring.
Music: ok, not the best, but catchy.
Rewatch value: I don't think I'll see this show again, except some scenes with the king.