Took two of the most powerful and badass characters in the show and combined them.. then turned her into a stupid useless damsel in distress for the whole season. I kept waiting for the moment she unleashes her powers and it never came.. when it finally came at the end, it was so frustrating and anticlimactic.. they just used it to set up season 2.

The 2nd most powerful character spent the whole season being missing. They kept building up for his return. At the end when all hopes were lost he actually returned.. then just died without doing anything!

The third most powerful character spent the whole show drinking chaste tea.

Jang's return, Mu-Deok's real identity reveal, Bu-Yeon's power to control the ice stone, Naksu reveal... All of them were ruined and nobody seemed to care about these reveal.. these were supposed to be the big moments in the finale. The only meaningful fight was in the very first episode. The finale didn't have any fight. They used the last Naksu fight as an end credit set up for season 2.

The last 4 episodes didn't even have 15 min worth of story. I don't even think a 2nd season was necessary.

Whoever cast the child actors for the 3 brothers must be blind cuz they look so different from their adult counter parts that it's not even funny.

Then there's the plotholes.. every single plotline was illogical. I think the writers had go through some intensive mental training to come up with those illogical excuses to stop Naksu from using her power and Bu-Yeon from controlling the Ice Stone. I am going to list a few of them plotholes here ..
1. Everyone blaming Jang Kang for using the ice stone when it was lady Jin who forced him to use it for her own gain.
2. Everyone can use the power of the ice stone for everything except Naksu and Bu-Yeon (who is supposed to be the only one who can control it's power)
3. Bu-Yeon, the most powerful priest who can control Naksu's power and stop her from running wild couldn't stop her from running wild after some weak spell from Ji Mu
4. Ice stone can stop every soul sifter from running wild or being petrified expect for Naksu
5. The whole ice stone barrier episode makes no sense
6. Lady Jin not confronting her husband and Ji Mu full well knowing her daughter is fake.
7. Even after learning that Mu-Deok could be her daughter she did nothing to save her.
9. How could everyone (including Songrim) just agree to kill Mu-Deok to see the power of the ice stone just like that?
10. How is Ji Mu still alive? It makes no sense. When everyone was confronting the queen, he was just standing there and nobody said anything to him.
11. Kept talking about how the ice stone can unlock Naksu's power and keep her from being petrified permanently but after she used it she was back to being Mu-Deok
12. Naksu never caring about who is the blind girl that keep showing up in her vision.. or everyone else not caring about what happened to the original Mu-Deok's soul.
13. Lady Jin letting Ji Mu enter Jijiyoung even after knowing her daughter is fake (atleast she claims that she already knew)

and I can just go on and on..

The whole cast was great, even the actors who played the smallest roles did great. Vfx, action and cinematography were top notch. Comedy was very good. The main idea behind the story was somewhat decent.. but if you pay even a little attention everything falls apart.

Overall the show felt like "2 hrs of foreplay and 4 sec of actual sex or even no sex at all"

PS: Don't ask how I know what it feels like to have "2 hrs of foreplay and 4 sec of actual sex"