Acting:
I LOVED this drama, Park Ji Hoon's acting was amazing, I thought I wouldn't like Hong Ye Ji's acting because I've only heard bad stuff about it, but her acting was good. Her character is an assassin, it makes sense why she wouldn't really be very expressive. The ML is either possessed or has another personality (I am not sure, but I think historically they'd say a person is possessed if they had another personality), he went through a rollercoaster of emotions throughout the drama and expressed them amazingly well, I especially loved his portrayal of Ak Hee.

Plot:
The plot was really unique for a historical drama focusing on 2 'brothers' trying to get the throne. A lot of historical dramas about Kings/Prince's have this type of plot, but this one was unique mostly because it had a very soft ML.

Sajo Hyun did not like violence at all and hated how horrible of a King his father was, and I don't think he ever changed, he just stopped being meek. He also did not want the throne, neither of his personalities did, one wanted to make clothes and the other just hated politics (though he was very good at it). Honestly, there wouldn't have even been a fight for the throne had the Grand Prince (the brother) just been a decent person.

I loved Ak Hee, I had SLS for Ak Hee, but Sajo Hyun grew on me later on in the drama when he started to develop a lot of the attributes I like about Ak Hee. Ak Hee was such a hilarious (and adorable) character. I loved his sarcasm and his attitude, he was a mood. He truly did not care about anyone but Kyera/ Yeon Wol, I hated that she never saw his feelings as sincere. Ak Hee is treated as though he is the human embodiment of greed, and nothing else despite the fact that he is able to feel love and pain. He was only treated like a human at the begining of the drama, but later on he is treated as though he is just an evil spirit, and not part of Sajo Hyun.

There were a lot of plot twists in this drama, you don't really know whether Ak Hee is good or bad , if anything he was just greedy, which made him anxious, which made him do stupid things.

I also did not hate the Princess Consort, I didn't like her at all at the start, but then you get to see that even though she is selfish, she is not a bad person and she is also not really the MLs love interest. She had a lot of character development despite not having much on screen time.

I think the only thing I did not like about this drama was how Sajo Hyun and Ak Hee did not even try to understand Yeon Wol's hate of Sajo Hyun's father. Her hate and revenge were completely justified, though the vengeance itself was not very satisfying.

SPOILER - Ending:
I loved the ending of this drama. I never expected a satisfying happy ending for this type of drama, but this one had one.
Though Ak Hee is sort of killed of (I interpreted it as Sajo Hyun becoming mentally strong enough to no longer need Ak Hee), by the end of the drama Sajo Hyun becomes a lot like Ak Hee, and the pathological lying and greed aside, Ak Hee also becomes somewhat like Sajo Hyun.