I have to admit I kept my expectations low for this drama despite its high rating here because, 1. The leads are idol actors, and 2. I'm not really a fan of xianxia dramas. But this blew me out of the water. The story was really intricate and the characters are well-written.

Story:
What I liked the most about the story is, obviously, the evolution of Wei Wu Xian's life from being known as a carefree genius, to a black magic craftsman, to a hated person, to a "idgaf does it matter after all" mature character as he took in what he learned in the world.

I also liked that aside from the main story, there are multiple side-stories where the other cast become more than just side-characters. These are the side-stories I like the most:
1. Coffin Town arc (Xue Yang / Xiao Xing Chen / Song Lan / Jing)
2. Wen Qing and Wen Ning
3. Jin Guang Yao's whole storyline starting from the little subtle scenes at the Lan Clan lecture
4. Lan Si Zhui

Characters
I think this is the strongest part of this drama. The characters unleashed the full potential of the story. What I appreciated the most about the characters is, as what Lan Xi Chen said, everyone shouldn't be categorized as simply "black or white", "good or bad"; what matters is the intentions of their actions.

Of course there are evil characters here but we were also shown why they ended up that way, e.g. Xue Yang and someone from the Chang Clan who cut his finger simply because the poor boy was hungry, Jin Guang Yao who had been verbally, physically, and mentally abused because of the circumstances around his birth where he had technically no control over, Wen Qing who seemed evil at first but only cares for her brother more than anything in the world, etc.

Wei Wu Xian's character is undoubtedly my favorite. His maturity improved in what I think are three phases:
1. Jiang Clan's playful young master where he has all the leisure in the world to pursue his moral principles
2. Yiling Patriarch where he had to turn back from everything, including his family and friends, because he wants to stand up for what he think is right + Him holding on to black magic despite everyone's criticism because it is the only thing he can do now
3. Post-reincarnation. You can really see here how he is no longer the young man who plays around and near the end, he even takes on an indifferent viewpoint towards the hate around him because it doesn't matter for him now as long as his conscience is in the right place and he has someone who believes in him.

Lan Wang Ji's development is worth its own show as well. First when he started to support Wei Wu Xian, he still managed to stay within the rules and stay respected by the clans despite his association to "evil". Then post-reincarnation, he just throws everything away to pursue what he thinks is right. Granted I wanted to see more of him without Wei Wu Xian, but his character was a great complement and support that the hero needs.

Acting/Cast
I only know Xiao Zhan from Oh My Emperor where he was swoonworthy but pretty stoic, and Wang Yi Bo as a K-Pop group member so I have pretty low expectations for their acting. But WOW I was proven wrong. Xiao Zhan embodied Wei Wu Xian well. Characters like Wei Wu Xian are so easy to mess up if the actor is bad, because he can simply be acted out as a good guy who can do no wrong. But Xiao Zhan's Wei Wu Xian is so complex and human and we can really see the different facets of his character, both the good and bad. Wang Yi Bo also did wonders to Lan Wang Ji because of his microexpressions. Not on the same level as Xiao Zhan, but really impressive for an idol actor. The other actors are also amazing, my other favorites would be Wen Ning and Jiang Cheng.

Over-all it was a really great experience and I really enjoyed their world.