I'm not very good at saying review but let me give my thoughts on the drama as an avid kdrama viewer.
-Story is well written. Solid premise, intriguing plot, well-rounded characters, and dismissible plot holes.

-Actors fits they're characters so well that I could feel the tension in their expressions. The minute details of how they express their emotions whooo! I'm blown. They really got them right!

-Music is good as well. It manages to make me feel more and be more connected in the story. But there were parts that they're a bit too loud for my liking, maybe it's just me.

-Rewatch value-yes of course I will definitely rewatch this but I WOULD ABSOLUTELY CUT the drawn out flashback like OMG it was frustrating to be honest. I've never missed characters like this! I CANNNNT BELIEVE HOW LONG THIS FLASHBACK IS -___- I'm not really that invested in their history because we viewers were not that dumb to figure things out without them putting so much detail in it. I'm more interested with what's going to happen in the future -____- I know they're important details as well but they dragged it on a bit too much for my liking I'm more than exasperated!

NEVERTHELESS OVERALL THIS IS ONE OF THE MOST ENJOYABLE FANTASY KDRAMA I'VE EVER WATCHED!!!