Most importantly I would like to start by stating very clearly - this is NOT a BL. If someone has advertised it to you as one, don't expect what you would usually expect in BL series.
Being part of the LGBTQ community (being gay) does play a big role in the series - it's a part of what some main characters are, the bullying and stigma around it moves the plot forward and one of our main characters has plenty of feelings for the other. But that doesn't qualify it as a BL by no means.

Now onto what has been so good about the series.

The plot is quite wonderfully crafted - slowly, episode by episode, as the characters learn more we too see everything falling into place and how everything is intertwined and connected. The series has both a mythical and supernatural element, rooted in traditional beliefs and religion, along with psychological horror elements and suspense.
Following a group of three teenage friends discovering the truth behind their school, the staff and their own powers is a thrilling adventure, intertwined with friendship and seeking justice for those wronged is truly an adventure.
For those who need a warning, it does come with bit of blood and injuries present, as well as guns and other weapons. As well as mentions of suicide and self harm.

The acting is truly great! Fluke and Singto absolutely brilliantly portrayed every nuance of Dan and Nai. The roles are serious, heavy and filled with the full spectrum of emotions and they both did an amazing job. I especially have to praise Singto - he did a truly phenomenal job.
The entire cast putting their all into this is definitely a reason to watch series alone.

If you go into this as a crime/mystery/supernatural series, I belive you will thoroughly enjoy it!