I watched this one as it came out, and as a result I was disappointed for a lot longer than I needed to be. However with this I hope others don't need to be, and that those who will truly enjoy this drama find it well.
NOTE: I added a whole star to the overall simply for the first ep which was really well done. And spoilers are general rather than being about specific scenes/plot points.

WHO THIS DRAMA IS FOR:
1. People who'd watch anything as long as Woo Do Hwan is in it
2. People who are all about aesthetics. Not just the actors/actresses, but also the costume design and scene comp is so pleasing to the eye.
3. People who have no issue with overused tropes, predictable plot twists, and romance that takes up half of each ep.

STORY ~ 3
This one had a strong enough premise, but starts to fall to apart at the end of the first ep. The first ep had the ideals for everything in this drama. The pacing was good, the characters distinct and somewhat likable, the dialogue told more while saying less. Starting from the end of ep 1 that attention to detail drops, only reaching such lvls of quality once in a blue moon. Many plot points were utter wastes of time as they didn't lead anywhere.
This drama also masquerades as Sci-fi when the writer clearly wanted it to be fantasy, using her usual deus ex machina to fix every.

ACTING/CAST ~ 3.5
--Screen time wasted on shallow characters, and star cast wasted because of bad writing. Protagonists win for reasons, and the antagonists look menacing on the outside but don't accomplish a single thing.--

Main leads: while the main male character was consistent he lacked depth, and while the main female character seemed to have depth with other characters, all of that went away when in the presence of the ML (AKA half the show). As for the acting, it's LMH as usual meaning you'll either hate him or love him (AKA he still hasn't learned how to act). Kim Go Eun gave a solid performance, but with how badly her character is written it's hard to distinguish if her cruddy scenes are due to inconsistent abilities or writing/direction.

WDH/Jo Yeong and Eun Sup: both characters are likable and have much more to them than many of the others. Also with a stellar performance from WDH it's easy to find habits, movements, and speech patterns (not just accent) held by one or the other.

Kim Kyung Nam/Kang Shin Jae: Thought he was gonna be a typical a**hole 2nd lead who was bitter from years of pining after 1st lead, however I'm happy to say that wasn't the case! In fact he easily stole the show for me. As much as I adore Eun Seop and Yeong, neither of WDH's characters had half the depth as Shin Jae's character did. He is such a well written character and he has the only satisfying character arc in this entire show. Kim Kyung Nam's portrayal of him was awe inspiring, really adding to the character.

Antagonists: The antagonists get a 1 star in total for the actors being great, however the two main antagonists accomplished nothing throughout the show.

Ensemble: There were some fun characters in the ensemble cast, however they were still under explored and some characters left me wondering why they were included if they didn't ever further the plot or have their own agency.

MUSIC ~ 3
I've heard it's got a great OST, but considering I can't remember a single word, nor any tune other then the opening one I can't rate this section any higher.

REWATCH VALUE ~ 3
Only worth it for specific scenes or if you can't sleep until you've figure out what the hell is going on.

TL:DR
Great premise but badly written. Great cast (for the most part) but numerous useless characters. A soundtrack that works but might not make you feel anything.

If y'all want specific examples or spoils lemme know and I'll spoiler tag them in the comments.