Listen, this drama has a really good incipit.
The story is inspired by "Journey to the west" they had the "romance" element and others details.
The first half(10 episodes) are really good. the direct has made some pretty good choices.
after the episode 11 the story loose sense.
The ending is probalby one of the worst in kdrama history.
First of all is an "open ending" so the watcher has to drawn conclusion in a really complex world building.
Secondo of is "the journey of hero" in every story we have a character that grows.
Son oh gong is a villan in the begining, so he has to learn to be a better person through love.
The problem is nothing really change at all.
In the begining he was a bad guy and in the end we have a bad guy with a love interest.
He didn't grows, he remain the same, this is really big problem, he didn't learn anything from his "journey".
So if you want a drama to watch when you are bored, this can be a good piece of entertainment.
But if you're looking for something with a good plot and a story with sense, this drama isn't for you.