I just watched the first season (the seasons are separate stories). It was honestly kind of disappointing. Some parts where really dragged out, and especially with the cult gatherings they just made you sit through almost the exact same thing multiple times. Really just made me want to skip ahead. The ending, however, was incredible rushed. That easily could have been several episodes. The order of the epilogue also seemed a bit random here.

Most annoying I found the "miscommunications" I had with this show. It gave the impression like they where going to do something, for example: "oh they're going to try and escape". But then it would just cut to the next scene with them just sitting in their rooms as usual and it was like "oh I guess they meant later". They ended up in the right places eventually, but the road too it just felt very clumsy, and the characters decisions could feel quite random some times.

I found the first few episodes to be much more exiting than the rest of the show, which felt much more monotone. At the beginning there was just much more going on. All the characters had these little side stories going on that make a show feel fleshed out. Later on it was just purely the cult and showing over and over again how brainwashed everyone is.

I also found it a bit disappointing that they never really explained the backgrounds of 'the spiritual father' and apostle Jo. Their motivations and the relationship between them was left kind of vague and made the story feel incomplete.

That all being said, the show wasn't completely awful. It had its moments. Just don't expect too much from it.

Regarding season 1:
I found it to be very flawed from all angles and it only served as a learning experience for those who carried on with the second season. Its portrayal of a cult lacked a compelling thematic foundation, opting instead to draw inspiration from cheap rip-off D-grade movies themed around cults. Where cults are extremely over-dramatized to the point of crossing the supernatural territory. The cult apparently possessed super powers of hypnosis with only a few words spoken, even towards people who weren't perceptible to religious and spiritual beliefs. Everything surrounded the cult came off as cartoonish even within the context of a 'drama'. The narrative itself struggled to carry its own weight, particularly as it primarily focused on the perspectives of the outsiders. It always felt as if it was building up towards something bigger but it never got there. For a 16-episodes run, it needed a proper world building and foundation for the cult. Establishing a distinct "character" for the cult would have provided a stronger identity. Back to the outsiders, having the drama led by teenage characters was another weak aspect of it. Bland and cardboard characters. The mystery element was a crucial part of the drama yet it was lacking and under-delivering. The first season would have fared better as a standalone one-off movie rather than a drama. It doesn't make any sense why the drama was rated this high, according to MDL standards, especially when season 2 effectively addressed most of the issues with the cult and delivered an overall better package!

Regarding Season 2:
It managed to deliver a much more compelling package than season 1. The most important part is that it handled the cult theme properly. The characters and the cast were a lot more appealing than season 1. Having a more adult leading characters rather than teenager was a plus. Uhm Tae Goo was a perfect casting choice for his character. The story had a better and more natural progression than season 1. However, it got sloppier the closer it got to the ending. Speaking of the ending, it was a bit underwhelming and not as grandiose as I hoped it would be. Second season should have been a stand alone drama unrelated to the first one, not even in the name. If you don't feel like watching two seasons then you can ignore the first one and just watch the second.