I've only watched a couple of episodes and dropped this drama because it was just unbearable to continue.
I first want to state that the production was done very well, from the set to the effects.

STORY: The beginning of the story really captured my attention. I really enjoyed how the story shined a light on mental health awareness since there are not many HK dramas like that out there. This drama was refreshing, concepts like serial killers and mental disorders aren't common in recent HK dramas. I really enjoyed how the drama showed what MC's mind looks like and the setup with his relationship with his sister and the psychiatrist. The drama did a great job showing MC's past and trauma and his strained relationship with his mother.

But there were minor details here and there that ruined the whole show for me. It didn't make sense that the MC was able to join the police investigation since he had no connection to the police. I'm surprised his original personality was useful because all he ever since was slack off and chase after girls. Madam Sing (FL) who was a bomb disposal expert, also randomly joined the special crime unit, even though that's not her specialty.

Also, I didn't like how they made MC's sister into a damsel in distress who can't do anything by herself. I would've been more okay with this if the story developed her original personality more since now she just feels like an empty husk without a real personality. The drama was too fast-paced in mending MC's relationship with his mother. Attempting to murder your children and abandoning them is not something that's easily forgivable. Also, the MC had a grudge against his mother for most of his life, so it was weird how he forgave her so quickly. Additionally, it didn't make sense how MC's second personality came back after he "cured his DID after making up with his mom".
And personally, the serial killer's signature green eye is just cringy and Madam Sing's outfit is questionable to wear while working in the police force.

ACTING/CAST: I think they did a wonderful job in the casting. They're all seasoned actors/actresses that starred in many past TVB dramas. They made the right choice to make Benjamin Yuen play the psychiatrist. He portrayed his character well, being well-mannered, friendly, but mysterious and off-setting at the same time.

MUSIC: I didn't really focus on the music, there weren't really any outstanding soundtracks, but I never once thought there was a song out of place.

REWATCH VALUE: I would not rewatch this drama, as you can see I dropped it not even halfway completing it. Throughout episodes 5-7, I practically forced myself to continue it, but I just couldn't see any more potential. Everything I enjoyed about the drama disappeared after episode 6 and I lost interest.

OVERALL: This drama had an interesting start that drew me in with curiosity, but it goes downhill from there real quick. The only thing that kept me going was MC's family relationship. I'm not sure if the story redeems itself or what I saw was just a small piece of the big picture, since I dropped it in the beginning and don't have the patience to continue.

However, I do think you should check out this drama at least once because it's something new that's not really seen in HK dramas before. Who knows, maybe you'll like it?