The spoiler is at the end and marked.

I concur with everything written by Shinnosuke_Lee, including the evaluation of the ending.

This was an INCREDIBLE show in all the ways that reviewer mentioned. Loved it all. They all were incredible performances. I double-foot stomp BIBI's performance. It was great and a needed breath of fresh air in the overall cast of characters. The story really is stellar with constant twists and edge of your seat drama. (When the violence got too much for me (as an older viewer), I just turned off the audio and/or covered my eyes.) The cinematography, the editing, etc. were phenomenal. I expect this to be remade a number of times by various artists across the world, because the story holds up so well and can be set in many parts of the globe. What more would you want in a cops-robbers/love story? I am surprised that the rating overall on MDL is not higher.

(I did have an issue with the Disney digitization which gave a slight green cast to the footage. This emphasizes the film noir effect, but I don't like it. I was a video editor, so most people, other than folks like me, will likely not be bothered by it.)

SPOILER:
I note that some reviewers think that the drug boss's motivation is money/success. I concur only in that he believes that this will win the love/respect of his childhood sweetheart, which is his ultimate goal--the same goal as that of the ML, which is to win the love/respect of his wife. (A reviewer compared the drug boss to Jay Gatsby in the novel "The Great Gatsby" and I concur.) The FL has "the face that launched a thousand ships," as they say of Helen of Troy. And I think that the FL lead was able to feel empathy (NOT love) for the drug boss, just as the ML was able to feel empathy for the Chinese drug negotiator--but the true love remained between the ML and FL, as evidenced by her continued pleads for him to be pulled from the operation.

Regarding the ending, IMHO the ML again sacrificed himself and his marriage for both the FL and drug boss, with whom he had developed a strong relationship. The drug boss had an "honorable" death and the FL didn't have to take the blame for his death. Therefore, the ML remained true to his character of protecting those that he loved, he didn't "turn evil." If the FL realizes this in time, then perhaps there may be a way for them to get back together.

Regarding the title of the drama, I wonder if the writer is trying to say that the worst evil is often the things we do for love. Did both men destroy themselves to gain the love of a woman? (Back to Helen of Troy) It is true that people do terrible things to protect their loved ones or to protect/foster the God they love or to avenge those that they love. Food for thought.