This drama did not leave the same impact on me as KES's work Mr. Sunshine . The story was all over the place, full of cliches, and felt unorganized. For the most part, if a drama has a bunch of cliches, cringe scenes, not so great story, as long as it has something to keep my interest, I won't complain much about the flaws. It felt like I was forcing myself to watch this drama and it took me a long time to finish this drama cause good dramas I usually finish in 3 days but this one took me 10 days. I was hoping that maybe that the start of the drama is slow and boring and it will get better in the middle but it wasn't till the last 4 episodes that actually brought back some of my interest.

The Characters /Acting & Story (spoilers start here)- Let me start this off by saying that in the main cast I have only seen LMH previous dramas & KGE's Goblin. I'm unfamiliar with the other actors.
This drama had the potential to be better, the idea of the story of a parallel world was a great start. There were just too many things that confused or angered the audience.
For example, the blatant advertising angered a lot, I found some of them funny but annoying at the same time. Most kdramas I watch always show the actors going to Subway or something and I know that it pretty much looks like Subway's sponsoring the drama, but at least time and dialogue are not wasted while trying to advertise the place. This drama had LINES promoting products. I saw LMH mention about 3-4 times about bbq chicken's being the best or another product being the same as his country blah blah. That is so unnecessary & unrelated to the story in a way. That time could have been used to explain more about the plot or have lines relating to the drama.
Now for the confusing part:
This whole parallel universe then third dimension with everything frozen along with time traveling could have been kept straightforward but the way they decided to deliver it throughout the drama was confusing. You get to know this parallel universe exists and it takes a few episodes to find out how it works and why time stops and for how long and then its meaning behind it a few episodes later. And then even more episodes later you find out sorta about why some of them have burning scars on thunder-storming nights. Then near the end you find out they can go back in time and multiple universes. I get they're trying to use the common method of slowly giving you answers which in most dramas I don't mind but it made me bored and only interested in the end to see how it ends. Another thing is they start off the first episode in a scene and in the last episode we're back in that same scene. I didn't mind that either. But then to do the same within episodes is triggering. I would start the next episode wondering if I skipped an episode cause it was not in order. They would randomly start somewhere and go back to connecting to that scene later on in the episode or next episode. And some scenes were never gone back to clarify.

WDH made his parts enjoyable to watch whether he's Eun Sup or Yeong. He was able to perfectly act out two different characters of the parallel world. I wished the directors/writers gave him more scenes/screen time. He's one of the reasons why I gave this drama a higher rating than most average reviews. He pretty much carried the drama by bringing "life" into his characters so I overlooked the fact that not much is known about these two characters. I wished they'd show some romance between him and KYJ instead. I'm sure they would have a better story and pull it off than the main couple.
As for JEC, I can't even say anything about her acting. She had minimal scenes with almost no impact. We know so little about her character in the drama as well. All we know is she's an ambitious person with a hunger for power and she's willing to do anything to reach her goals. The writers make us assume that she's like this because she wants to climb up in the social status ranking because she has this inferiority complex that she started out at the bottom with nothing. That's a very typical reason and at first she's shown out to be a strong female character but turns out its the men in the story (her husband, advisor, etc) that helped her to get that far in the social ladder. Then they show how Lee Lim also wanted to use her and it seems like she just gets outsmarted by every guy in the story. They imply that she cares for her mother, but there were no scenes to feel that mother-daughter relationship to begin with. And we know nothing about her doppelganger character at all.
KKN's character was somewhat better. I could feel his affection with his mother & Tae eul. Although there are some things I do question about the writing of his character. The villain was a flat character. Not going to go into depth in the review it will be too many spoilers already.
As for the main couple everyone had this criticism regarding their chemistry. I feel like they would have better chemistry but because of the crappy writing and the flow of things it wasn't pulled off well. I think this couple would have been better if the writing/story was adjusted a bit. But my critique is regarding their characters. I will admit watching KGE in Goblin made me question if it was her acting that's bad or the role given to her. In this drama, she did a lot better. It's true she didn't pull off the two characters differently in the way WDH did. Luna's way of talking and Tae eul was pretty much the same. One just had different tastes in clothing and hair than the other. I also hate how this drama portray its women (complete opposite from Mr. Sunshine in that sense at well). It's already tiring to see every media whether Western or Eastern portray women like this. They show Tae eul as a police detective with a black belt. She's admitted at times to be scared, but have to be brave and she wasn't afraid to get to the bottom of something or hunt/run into somewhat dangerous criminals. But in that one scene where she gets stabbed, they show her not using her skills as an officer and black belt user. As an officer, I'm sure you will be aware of what dangerous situation you're in and you have to be on watch. They just went from showing a strong female to a weak female in a situation like that. I would get if she's outnumbered. But in another scene she was strong enough to get herself away in an outnumbered situation as well. I also felt like she would play a major role in the drama and contribute to helping Lee Gon out, but they even take that away from her. She's basically shown in investigations and as the love interest of the male lead. I don't mind seeing a FL in love with the ML but at least showcase her strengths often and make her more useful in the story.

Overall, the production was high quality and music/OST's were amazing, but there were countless flaws in the story. If you can overlook these flaws in the story, and watch for minimal entertainment and some action then you'll be fine. Although for me this only got interesting near the end when things were going to be tied up and supposedly explained clearly. This drama makes you end up crafting theories for multiple things.