I had a careful think before I started watching this. I'm not always into anything "fantasy" and time travel can be a difficult thing to pull off. Combine that with serial killers and it could be a bit dodgy. I read a number of reviews before I made the decision to try this and many of those were to say the least, "mixed".
On the whole I enjoyed this drama, though it of course is not perfect. However, when I try to put down my thoughts and reactions, all I manage is a bit of a ramble that makes this sound worse than it was. But for what it's worth, here it is ....
The idea didn't at first appeal to me, but in fact I think that it was quite well handled. Someone said that they had Park Gwan Ho adjust far too easily into the 2016 world, and could have made much more of the culture shock, and I agree. They completely glossed over the impact of the mobile phone on a Detective who worked for 10 years with only paper forms, or police radio to rely on. They made no reference to the fact that in 30 years, laws and police procedure will have changed enormously. But that's not what this series is about, though I think there should have been more acknowledgement of it, and also appreciation of some of the "old-fashioned" skills.
The serial killer/police/psychologist triad is not particularly new, and it was all OK. Disappointing to see the tired old really boring device of the killer targeting the female profiler AGAIN!
I found it unbelievable that in 1986 Korea did not know about serial killers. I can believe that the authorities did not want them to get any publicity, but I absolutely believe that the police would have known about them. These were not stupid nor venal uncaring men.
Another issue really, for me, is the pacing. There were long pauses in dialog and plot. Lots of fists flying around in the dark where you can't really see what's happening, fruitless chases through twisting alleys. I'm not even going to touch on the plot holes, which I was happy enough to ignore. FF came into play a lot.
What I did enjoy was the tiny hints about 1980s attitudes rubbing up against the 2010s - really there should have been many many more of these - the nearest we get to any sense there is an issue is the joke that Gwan Ho needs to go for training (which he DID need, but never happens).
I also very much liked the "bromance" between Guan Ho and Sun Jae - and with the rest of the team too.
Lee Yoo Young as Jae Yi was endearing too, though I'm not sure there was much chemistry - it was OK.
There's not much demand for logic in the police investigations, either, and damn all thought given to rules of evidence or securing a conviction in court. This drama does kinda follow a 1970s The Sweeney interrogation roller-coaster, and there's a lot of men running around without a clear strategy ... going off at half cock. Brain not fully engaged. That got a bit frustrating. Hence quite a bit of FF, too.
There is, for my taste, a bit too much schmaltsy music conveying emotions that the cast are supposed to emote, in place of actual writing, but others may like it. Not me. The emotional 'departures' at the end were a bit too much for me and could have been improved with even a slight consideration to explore the uncertainty of exactly what would/could happen in the jolly old time-space continuum, and whether the future would actually be changed when Guan Ho's does NOT stay disappeared ...
Writing this, I realise it sounds like I didn't enjoy this story, there's such a lot wrong with it. But somehow I did quite like it, and I'm not really sure why. If forced to figure out why, I think the male leads especially, and investigative team have enough charisma to engage the viewer - well, me. There were elements of humour, as well as pain and a range of emotions, very nicely handled (though, again, a bit of FF - sometimes just a bit to slow paced for me).
The pacing is down to the Director and Writer, and yes, I think this drama could have been presented very well in as few as 12 episodes, maybe 14.
The alternative would be to include a range of other cultural issues and "educations" for Guan Ho, and show the kind of investigative skills required when you don't have DNA and technology to bridge the evidential gap. And I don't mean throwing a tant and beating people up, I mean, actually talking to people, listening and persuading them to talk to you and tell you stuff that even they may not know they know ... and then making the connections between apparently unrelated bits of information - we could have had a lot more of that! I wondered if that would make it a different series, but actually I don't think it would have, it would in fact have fitted very well with the premise and enhanced the story a lot.
But, yeah, still, overall, not bad.