A time travel story, the two main characters go back in time to a town with events (a murder mystery) and people important to their lives. The pacing of the mystery was quite good, it was slow but in a good way.

Pros:
1. The mystery was done well, and I never felt frustrated thinking that something was happening just to extend the plot. This was mostly because the ML had interesting relationships with everyone else in the town, so just seeing those interactions was worthwhile.
2. The actress who plays Ko Mi Sook was terrific. In general, I thought the acting and characterization of most of the female characters here was really good, and you generally don't see that in serial killing shows. Lots of characters I wish had more screen time.
3. I liked the ending, it wrapped up a thought I had the whole time watching. I only remember noticing one plot hole, which was pretty good for a time travel show (a lot could have gone wrong).

Cons:
1. The writers let the FL down. Her character wasn't that interesting, her relationships with the people in the town were underwhelming, and at some points I wondered if a version of the show that just didn't have her (but gave more time/importance to the other female characters) would be better. It felt like she was just a cheerleader for 2 people, rather than actually being a part of the world. But she wasn't annoying either - she was just there.
2. The romance. Just why? Came out of nowhere and seemed rather pointless.
3. Show, don't tell. I would feel cold listening to the ML talk about his life with the FL. But then when the ML would actually interact with important people, those scenes were really compelling. Especially for a 'mystery' show, I wish the ML would have explained himself less, so that there would have been a bit more emotion and suspense.

In the end, this was a solid, quite consistent, and enjoyable show.