The storytelling was masterful - I like how it explored the themes of humanity, evil, morality, and did so in a very subtle manner. While I did think that there were some minor plot holes (ie. with the murders that Dong Sheng committed, he should have been more careful with fingerprints as it felt like he was getting away too easily), overall the drama is probably the best cdrama this year so far and will be one to remember for years to come!
Chao Yang - In one of the starting eps, an illustration of the wolf killing the 3 pigs and seems like this is pointing to Dong Sheng being the wolf but in reality it is really Chao Yang, because he's the only one who is surviving at the end of the drama (if you are choosing to believe that both pupu and yan liang died). At the end of the drama, viewers can see that Chao Yang is a master manipulator who slowly reveals how scary he really is - ie he kept feeding lies to the police, when he found out that his dad was recording him secretly, rather than getting mad he went on to put on an ACT and manipulate his dad into feeling bad, and also when he kept lying to Dong Sheng and wasn't honest about the duplicated clip, etc.
With that said, I think the drama tried to humanize him and make him a 'relatable' character esp at the beginning when we all think that he's being bullied and ostracized by his classmates. Looking back now, it's probably Chao Yang who is alienating others and lacks the capacity to relate to others. I think this drama really makes you think about what makes a monster - the age old debate of nature vs nurture. Arguably monsters are not born, and you can see that his family environment has created trauma for him growing up - his neglectful and cold father, his rude step mom and step sister and finally his own mom who often leaves him alone for work and is overly controlling. On one hand you almost feel bad for Chao Yang and he's almost an anti-hero in the sense that you WANT to root for him and you want him to come clean at the end, but at the same time he manipulates those around him and almost shows a complete lack of remorse for what he did. Someone mentioned this under the comments but this is akin to a villian origin story - a deep exploration into the backstory of Chao Yang and his upbringing. Will be so interesting if the story extends to 10 years later and we see how Chao Yang has matured and grown into an adult; if he ends up being a serial killer like his predecessor Dong Sheng or if he somehow finds a way to crawl out of the dark hole of sociopathy.