Tons of spoilers ahead!

In short: absolutely fantastic.

MCW and LJG knock it out of the park with their acting. LJG especially–the scenes in which he breaks down and bawls his soul out, especially contrasted against his normally stoic and unruffled character, is brilliant and hits you right in the heart.

In terms of character, Hyun Soo and Ji Won are nearly perfect. They're an absolute power couple. Ji Won is smart and a capable detective, with seemingly unending love for her husband, and the trust she has in him is admirable. Hyun Soo is so painfully misunderstood. When I watched the first few episodes, I was truly confused about how they would make Hyun Soo a likable character (especially after he'd kidnapped the reporter), and the writer went above and beyond. They transform Hyun Soo from a frankly intimidating, cold manipulator into someone who's been manipulated his entire life, by his father, his neighbors, his fake parents, the entire country, to the point where he doesn't even know who he is anymore. His emotionlessness makes him a tool to everybody else's desires, destined to mold himself to satisfy others; in reality, it's a trait hammered into him over a lifetime, and it's heartbreaking to see him discover love and pain and sadness for the first time, and then latch on to them so tightly (to the point where the thought of losing Ji Won tears him apart and nearly pushes him to the brink). He's really internalized what everyone tells him, like how he gradually starts to imagine seeing his dead father because the villagers all think he's possessed, and isn't that feeling, that you care so much you believe what others say of you?

And then it's doubly heartbreaking that, after all of their emotional growth and the challenges they've had to overcome, Hyun Soo sacrifices himself to save Ji Won and loses his memories in the process. At first, I was frustrated–another amnesia plot? But it gradually made more sense as the episode ran: Hyun Soo has never lived for himself, /truly/ himself, before. And Ji Won has never had the chance to see Hyun Soo for who he really is and make her own choice. The memory loss gives them both a chance for a new start, and it's heartbreakingly sweet that they choose to take that chance with each other, together. They have to restart from day one, without 15 years of a life together, but the pieces are there in shared moments and memories. For all of Hyun Soo's lying and manipulation, he was lying to himself too, that he felt nothing when in truth it was always Ji Won for him.

The reporter is great too, an unexpected source of levity in an otherwise serious melodrama. And I was particularly surprised and impressed at the last speech he gave to Hee Sung's parents about being complicit in evil acts (I honestly thought he was gonna get killed lmao). Ji Won's police squad are all awesome: I came to love all of them (even the annoyingly nosy one), and I'm so glad there was not one bad, two-faced one among them. Hae Soo served her purpose and I'm glad she ended up where she did, but ultimately she was the one character I wasn't fully sold on. She just wasn't as compelling as everyone else.

Of everything, the one thing that frustrated me was the lack of communication, especially on Hyun Soo's part (and partly Hae Soo as well). He always had to do everything on his own without telling people about his plans, which often led to dangerous situations or misunderstandings, especially between him and Ji Won. It's understandable that he's been taught to trust himself and has deeply internalized it, and makes it even more of a significant achievement when he reaches out to Ji Won for help. But other times, even after they've established trust, he still goes behind her back, and the viewer in me wants to reach across the screen, give him a slap, and tell him to just share with his damn wife already!

The story really just kept chugging to the last episode, where it slowed down (but the last episode was still great in terms of wringing some really emotional scenes out of the main pair). I was so scared of reading spoilers because I legit had no idea where the story was going to go. The accomplice had me constantly guessing in the first half (even when he was finally revealed, I was still suspicious of other people lol). And then the accomplice turned out to be a master planner and DHS + CJW kinda let me down in their planning abilities but we just accept it lol.

Cinematography is bomb. The OST is BOMB. I've been playing Feel You by Shin Yong Jae on repeat for days. IT'S SO GOOD.

Overall, definitely one of the best dramas of 2020. Would I go through the wringer and rewatch it again? Idk, it's just such an emotionally taxing drama (in the best way possible). But if I ever need a tearjerker, I'll definitely rewatch the scenes when LJG and MCW bawl their hearts out.

A few remaining questions:
1. Hyun Soo said he didn't remember any of his life from before he was 10 years old. I wish they explained this more.
2. Ji Won did find a bloody zip tie in the basement when she first got suspicious, but it seems to have been just glossed over. Why didn't this prompt more suspicion / questions?
3. What happened to Jeong Mi Sook (the last victim) + her husband?