As for the negative reviews, ignore them. Someone said there were no character development and the fighting scenes were not really that good- well I guess it is a personal reference. I think the crown prince's acting toward the fighting scenes were actually accurate considering crown princes were very sheltered at that time, they might had training but it will always be different on actual battle. In usual k-dramas crown princes are usually straight up good at everything esp in sword scenes which well made it in our heads but Kingdom has shown such diversion- Chang slowly gets better. Also, significant characters??? No. All of them played a role in the build up for every scene, I guess it really becomes overwhelming for someone who isn't really into the drama.
Also, someone said, the evil doesn't know how to act evil, they just act selfishly. Bruuhh I was so frustrated at this comment cause I was annoyed at the villain's selfishness, well what is the root of them being evil in the first place? How do you expect them to be evil?
Another, the main characters make stupid decision?- It is wasn't really stupid, it was actually realistic considering that this happened at that time- there were no ways of proper information dissemination and blah blah blah.
All in all, the frustrations in watching actually makes the drama more interesting as to how they dealt with such happening that time. It is a great production and I was actually glad that the villains did die- that was so satisfying it would have been cliche if the villains lives till the end and its on a repetitive cycle.