I generally love crime thrillers but Decoy bored me so I will just list some of the reasons I disliked the series first.

1. There is so much back and forth time jumps. Aft first, I found it hard to keep track on how far they were going back as the story takes you back to different years following the story of both the victims of the scam as well as the fraudsters. After a while, I just stopped caring and just wanted the story to move forward.
2. Most of the story takes place in flashback. It would be easier if we got the back story and then saw the person in the present. They would show you a dead body and you would have no idea who they are. Then after awhile they would go backwards in time with reference to the dead person and I found myself thinking. "Okay, this person is dead so why do I need to care what their role was?" I wasn't invested in them anymore. I wish we got to see their back story first.
3. The whole tone of the show is dull. The scenes shot in the present have a blue filter and the past is in a yellow/orange filter. The way the actors speak all feel a bit monotonous especially our lead detective.
4. Again because the story is working backwards, I didn't feel a connection to the victims early on. I wasn't fully empathetic to their suffering. Instead I was impatient to figure out if they will get their justice in the present but instead I was forced to go back to the past every time something interesting happened in the present.
5. It also adds to the frustration that the lead detective keeps undermining the victims of scam saying it's not a big deal compared to murder and refusing to look into any possible connection to things happening in the present. At the same time, he wants to get information out of them while also name-calling them. The last thing you want the male lead to be is a jerk and those are the vibes that I got from him.
6. Just when the series was getting somewhere in the present, it ended. I am okay with splitting shows up but for Decoy, it doesn't work in it's favour. Maybe my impression of the show would be better if it was complete rather than being divided in this way.

What I liked:
1. The female lead who plays the reporter. She is clearly a smart character. Smarter than the detective in fact and she picks up on things fairly quickly. Acts in the nick of time and was the main reason I enjoyed this series.
2. The only person I developed some sympathy for was the "oppa" of the female lead even though he didn't get much of a role. Rather there were only glimpses of him.
3. No Sang Cheon, the con artist. Loved his character. He feels more like a grey character than a pure bad guy. To some extent, I admire his wits for catching on to a scam. That's a different matter that he turns into a scamster himself. He also seems to be the only character that actually portrays the widest range of emotions and has enthusiasm when he speaks.

Even 6 episodes took me a long time to cover as I would start feeling sleepy so to prevent that I had to watch the show in 2x. I will watch part 2 just for the conclusion and I hope it will be more focused on the present for a change.