The only valuable thing ( rarely achieved in Korea cultural thief dramas) is the representation of the Ming armor, mostly accurate that the news was even spread on Chinese medias.

But it's the really the 1 only thing valuable.
Historical inaccuracy both in historical fact and depiction of the reality. Japanese are depicted as cowards, and Chinese are greedy and arrogant. I should mention even the problem in speaking in Japanese and Chinese ( a student can speak way better). "Lao Ye" in a non-confidential relationship is unbearable to listen, and the depiction of a modified relationship from mutual respect to contrast is too stupid.
The big problem is that the depiction is like Korean army pretend to be able to defeat Japanese army on their own, in a showing act of supreme arrogance while it was them to ask for help to the Great Ming Empire, their sangguk, their master and owner.

The whole drama diminishes and degrades Yi Sun's sacrifice because Korea is too arrogant in their own depiction.
A show completely to miss, because it only show arrogance.
But don't be surprised, don't you know Korea created the whole world, as they themselves are convinced?