Actually I'm pretty impressed with this show. What originally caught my interest in the show was 1) Kim Bum (KB) and 2) Lee Kwang Soo (LKS). I happen to like a few dramas that Moon Geun Young (MGY) has been in but as a general rule, I'm not an avid follower. The first episode isn't too impressive. I don't know if it was the subtitles necessarily, but (as most Kdramas generally are) the beginning was a bit slow but I'd rather have that than what "The Great Seer" did and in the span of 1 episode cover 20+ years. Anyway, the beginning was a bit slow but episode 2 is where it picks up. The first 5(1/2) episodes cover the characters younger selves and no scene was wasted; if the scene wasn't covering character development, it was covering plot development and I felt that the writers mixed the two very well. The characters become very endearing after episode two and by episode 5, I wasn't quite ready to move on to the adult versions, even though I love to watch KB & LKS act.
As far as the characters go--I feel like they're all portrayed very realistically. MGY's character isn't perfect, she's flawed--not flawed enough to be "how-are-you-still-around" annoyed, but as a young woman stuck between a rock and a hard place and having to make decisions. She's honest and naive but yet strong at the same time. (If anyone has seen as far as episode 4, the scene where she is speaking with the King), that is her characters defining personality; she has a strong need to right wrong's without appearing weak. Mad props to Jin Ji Hee (MGY's younger counterpart) for her impressive acting skills in the beginning. Prince Kwanghae's character is also very likable. He's human so he gets annoyed, he gets angry and scared(again, referring to episode 4) but he always tries his best to protect as many people as he can but he doesn't do it in such a way where you think "I give up on you, you're hopeless!" before throwing the remote at the TV. BUT the character that I'm thoroughly impressed with the writers about is the main...bad guy? Jeon Kwang Leol's portrayal of Lee Kang Chun is probably the most realistic of them all. In most Kdramas, the bad guys are purely bad guys. They very rarely appear human, they just hate and hate and hate to the point where you kind of wish they meet a terrible, gory death via a gaggle of gangsters prepared to unleash a sledgehammer beating but this isn't the case with Lee Kang Chun. He's a character that is good at his job and knows how to play the political field and help maneuver things his way--if he needs too--but the love he has for his son is "hate to love him" redeeming quality. I mean, he's without a doubt, a bad guy but you'd be ok with him spending the rest of his life in prison where he can see his son.
So, moral of the story...the first episode might be a little tough, but if you can get through that episode, I don't think you'll be disappointed. Give it a shot, by episode 10, you'll be cursing about having to wait 7 days for the next episode.