Let me just start by saying that while I enjoyed the first season I didn't love love it, but was very interested in the second season just because of what was teased at the end of the first season and what the trailer seemingly promised: Dark Shen Yi. I wanted to see Shen Yi go down a darker path and somehow claw his way out with the help of his friends and colleagues, but that was not what we got.
Dark Shen Yi aside, I at least want to be entertained by the cases, but holy moly I really wasn't. The first season had this problem (for me) too. The cases are easy to predict and the actual police work boring to watch (other than Shen Yi and his drawings).
I sound really bitter, I guess I am because this drama has all the threads of an exciting and interesting show, but they continually fall short, just giving the bare minimum. Everything felt so surface level and not deep in the way that I think they're trying to be. I think I'm most disappointed by it all because it feels like the writers/directors are wasting an excellent characters and ideas.
Also, I know there's talk of a 3rd season which I would check out because they pulled me back in with Evil!Shen Yi. A twin? A long lost brother? Who knows. But what I do know is that while they've set up something so interesting, I doubt they'll do anything really worth while.