Pros:
1. Good storyline which gets better with every passing episode.
2. Nicely paced. The drama has its fair share of slow moments. But personally I think they were necessary as breathers.
3. Great music. The music was honestly one of the most enjoyable factors for me in this drama. There were a lot of variations in music depending on the situations which complemented the scenes.
4. It is kind of a historical Mafia style drama.
5. Great friendships, great romance and great family bond.
6. Lots of emotions.
7. Satisfying.

Cons:
1. Big drama. It's 30 hours long with 1 hours each episode. But as I said before, it is nicely paced and it gets better with each episode. So even though it's a big drama it's definitely worth it.
2. A bit of fantasy aspect in it which honestly speaking wasn't entirely necessary. Even though it plays a big role theoretically, it was mostly ignored most of the drama. Honestly I feel like they could have achieved the exact same drama even without the fantasy aspect. But again, the fantasy part isn't too big and it can be enjoyed as a non-fantasy drama.
3. Did I say good music? It has sick music. I know it's not a con but I wanted to mention the music again anyway.

If you are into historical drama and even if you are not it's a must watch.