I really loved the drama towards the beginning, but I felt like it fell off over time. A lot of the plotlines felt half-baked and/or forgotten. The main plot could have used a lot more development. Like, I didn't really feel the pain the main character had in relation to the first life. I think some of the other lives were well written, but overall, there was a lot more to be desired when it came to the past lives, especially the first one, which was supposedly the most important one. I loved the acting, cinematography, and some of the locations were beautiful, but the story itself had so much potential.
I think Hotel Del Luna is a good comparison here. I was invested in Jang Man Wol's story and suffering because I thought it was well-developed. They took the time to tell her life's story through the flashbacks and I actually felt her suffering, although I also think that's because IU is a terrific actress. I think Shin Hye Sun is great as well, but they could have utilized her range better, imo. I'm going to read the webtoon now because I heard that the story there is much better.