I only watched this show because I liked period pieces, however I'm not a fan of crime dramas so I nearly skipped over it. I'm very glad I didn't.
I had never seen Allen Ren (Ren Jiu Lian) in anything before and Wow i'm glad I got to see him in this. He played Lu Yi fantastically. Not only the 'normal' Lu Yi who as the second in command of the Jin Yi Wei, a pretty emotionless and stubborn buy. In fact Lu Yi is actually introduced in a way that is more traditionally that of a villain than a hero which show how dark he is at the beginning. However AR also plays the character going mad as well as regressing to a childlike state (which I had to say I found cute) and not many actors could do such a thing. The actress playing Jin Xia was also great in how she balanced a strong female character with her almost childlike personality.
The chemistry between the couple was amazing on screen (I have heard it said that AR has no kissing clauses in his contracts, well he didn't in this show), you could tell just from looks and simple touches that something was going on and the two characters were meant to be together.
The costumes and music were also fantastic as were the sets. However there were things that let this production down a bit.
The story started out great and was something very different to most shows, however it soon turned into the well used 'my family hurt your family and I need revenge' trope that people can see coming a mile away. This change in direction ruined what could have been a really good story and made any surprises for the audience impossible.
Also some of the secondary characters seemed a bit two dimensional to me. Xie Xiao in particular never seemed to evolve much, all the way through he was obsessed with what he wanted and never seemed to understand anyone else's feelings. First it took him far to long to understand the basic concept that running away from his wedding might hurt the other person and then he took far too long to understand Jin Xia didn't like him (despite her telling him often enough).
Little things like that can make this show rather annoying in places but generally it's a fantastic show to watch, especially when it focuses on the two main leads or is early on when they are simply solving crimes and the cliché storyline hasn't come to light yet.