It starts off with the usual Joseon settings - power fights and intrigues among ministers, a girl in men's clothing with nobody doubting her fake gender, greedy mother and fights for the throne. So far, nothing new in the Joseon universe.
What's new is the mature figure of the (future) king, hilariously interpreted by Jo Jung Suk, the lack of silly dialogues, weak women fainting or loudly crying their souls out. Instead we've got strong, determined female characters and are introduced to the game baduk which the FL is a master of. The whole series is more mature than comparable ones, thus has a slower pace and more mature dialogues. Also the empathy needed for tactics in playing bakuk finds its counterpart in (but not limited to) the behaviour and speech of of the main leads.
All characters are very well acted and believable, the story is told with subtle details, also distinguishing between the king as a private person and being king as a ruler, adding a lot of depth. Or wanting revenge while loving the person, willpower and heart, making the inner struggles of the characters really felt.
This series kept me hooked till the end. I was living with it, wondering how to get out of this or that situation, alternating between there will/won't be a happy ending, hope and despair. The actors, the script, the suspense curve... really well done!
Even if you've watched a lot of other Joseon era movies, go for it. It's well worth it!