"The Client" is a mystery thriller court drama, with many red herrings that plays on familiar legal drama tropes. Within that is serious questions about justice, and the way to go about getting justice. As well as what general social consequences there are when a method to get justice goes wrong.
To contrast with the dramatic moments is criminal defense attorney who doesn't take himself all that seriously. He probably could have his own tv show, he's quite intriguing! His assistants as well have a lighter manner, creating some almost sitcom moments.
I would say this movie does a good job fleshing out both sides of the faults and issues of defense and prosecutor attorneys. I don't know the Korean justice system that well, but some of the calls the judge made, and the objective as well, seemed odd however. I have my doubts about whether "The Client" is that technically correct legally speaking. Especially the end. But I think there is enough nuance to make the movie philosophically interesting.
A bonus is the unexpected twist at the end. Kind of wish maybe it played out differently. But I do enjoy the banter between the two attorneys representing different sides. Maybe their relationship is the actual point of the film.