I binged this on Netflix recently and I did really enjoy it, but this is not without its flaws.

What I liked:
- really high production value - every scene looks as though it came from a movie, and not a TV series. The colors! The quality of the footage, the shots used!
- very strong opening, I binged the first three episodes immediately
- really interesting premise, drawing on Korean myths and folklore
- Lee Yeon and Lee Rang's relationship as brothers is just so good; Lee Rang kind of stole the show, honestly. I actually wanted to see more of the brothers than the main couple lol
- loved the parallels and themes between the different characters, and how this story was about community, and resolving the past
- heartwarming characters: I pretty much like all of the characters. Lee Yeon was a really fun character, Ji-ah was awesome (for the first five episodes), Granny's arc!!, Lee Rang, Ki Yu-ri, the little kid...

What I didn't like:
- a lot of plotholes. Some of the episodes baited you with an intriguing mystery that actually makes no sense in retrospect (car crash at start, Ji-ah's parents going to the cave when her mom was pregnant with her) although it makes for really good TV coz it's dramatic and suspenseful
- the two leads kind of had very little chemistry. They were cute, and I did like them, but you kind of look at them and think that the two of them are friends and not in love?
- Ji-ah had the same fate as Feng Zhiwei from The Rise of Phoenixes: really likeable, strong, had her own story and personality in the first half of the show, and then devolved into an accessory to the male lead/damsel in distress/only there for the romance in the last half. It was really a pity. She was so likeable and awesome in the first half
- cast for the villain (Imoogi) was really weird; he seemed like an emotionally awkward high-school boy. It was hard to buy into him as the final villain

TLDR: I grew really fond of the characters by the end, although the plot and logic of the show is really spotty at best