It's basically the story of Park Changho, a lawyer who is, we can say it, a loser in his job. He is a talkative person and, because of this people call him Big Mouth. He is involved in a murder case and he is somehow accused of being the criminal genius Big Mouse. Due to this, Park Changho ends up in jail.
Meanwhile, Go Miho who is Park Changho’s wife attempts to clear her husband's name.

I'll be honest here, I must say that this kind of show is really great to follow when they are airing, because not only despite the wait it's so much fun to try to guess who is the mysterious antagonist, but it's great to exchange so positively on MDL, week after week with those who like me followed the series. I love that this series managed to make us ask every week who Big Mouse is instead of us being able to guess it easily.

Big Mouth is more light-hearted type of thriller, there definitively more a family and romance theme even though they don't take much space, the production had rather intense tones while having also darker tones.

As for history itself, I think it is separated into two distinct parts.
The first where our protagonists meet, the situation and mysteries unfold, we learn more about Big Mouse. Then, there is the second part, where Big Mouse is revealed and the events accelerate for the conclusion with the development of several storylines at the same time.

I must say that there were a little criticism for part two coming from some viewers and I think it comes from the revelation of Big Mouse. The thing is, we are tricked by the show several times thinking that a character is Big Mouse when they are not, thus when the real Big Mouse appeared, people have continued to theorize on who is Big Mouse even afterward because for them, the revelation was disappointing, they couldn't believe it.
I'm going to be honest, in terms of script writing, the Big Mouse that we have revealed does make sense. On the other hand, in terms of character, I expected someone more charismatic to be honest. And this is where I realized that the series ultimately was not about "Who" is Big Mouse, but how it will link with Park Changho.
The series made us understand, and this from the start, that Big Mouse in truth is replacable, everyone could be Big Mouse, what is more interesting is how we go from there and how our main character blends in all of this. I don't want to give spoilers, but we quickly understand how the series will evolve after the revelation of Big Mouse.

This series is a "general public" thriller, although there are many elements of thrillers, it is still the genre that can be enjoyed by everyone and very entertaining. Now, the entertaining side is double-edged because clearly, that reduces realism.
There are so many scenes which are well played but which are purely fiction. While the series like "Through The Darkness" released this year, may be come across as less "entertaining", but it is a dark thriller filled with realism, it is not for all audiences. Same for "Insider", who by the way, has a lot of similarity with Big Mouth in the storyline, and the series is much more violent, with the inclusion of striking scenes of realism. These are thrillers that are not targeted or made for all audiences, I think Big Mouth is made for everyone despite certain scenes, and therefore its very entertaining aspect.

If I had to talk about the series, I would say that this one of the most captivating series of this year, we have been hooked from the start to the end, the writers did an excellent job to make us theorize during several episodes the hidden identity of a criminal, and not to mention the side storylines.
So I think that with Insider, Through the Darkness, King of Pigs, this might be among the best thriller series I saw this year - so far, maybe not the number one spot - but my opinion is biased by the fact that I like dark thrillers - but this series is definitely not to be missed.

Now, the acting et characters. Park Chang Ho is typically a character that will evolves quite quickly - maybe a bit too quickly for my taste, the evolution of his character is really entertaining though and it's one of the best highlights during the first episodes, we certainly don't get bored.
I want to mention Lee Jong Suk's acting, it's an actor that amazes me the more I discover him, and his roles are really varied in general. Here, his versatility was really incredible, he was able to show us many sides to his character, which I really enjoyed.

Also, I would like to mention Im Yoona, and although she didn't have as much depth as Lee Jong Suk, she managed to shine, and for once, I didn't dislike the female lead, she was able to be both strong and vulnerable, she was loyal, fierce and her character is really solid and consistent throughout the series, she supported Lee Jong Suk's character really well.

As for the rest of the cast, we have everything, endearing, captivating, detestable, funny, evil characters. No one, even the minor roles let us indifferent, we either love or hate them, but they are making us react to them.

Also, this series managed to make me hate characters that I loved at the beginning, and make me love characters that I hated at first, which to be honest is rare because I usually get dead set on my opinion on the characters. First examples, Jihoon and Doha. Jihoon is quite detestable at the beginning, and I must say that in truth, after a little hindsight, he was not that bad, just very determined. As for Doha, he is a fascinating character, and I didn't like to hate him in the end but he showed, I think the most change and complexity than all the characters in the series, even more than Park Changho.

Lastly, for part 2, because as I said, instead of revealing mysteries, the series created others plots, which at that time I thought was in preparation for season 2 or additional episodes, but no. So the only negative criticism I have is about the last two episodes. They wrapped up things poorly and quickly while the series was so well crafted until this point. The end was done in a matter of minutes, also they introduced the possibility for another character but in the end, he never made apparition nor given any time which is odd, so a lot of side plots are left in the wind. Plus, the stories of brillant characters ended badly while it had so much potential.

Do I recommend ? Yes, I think those who enjoy thrillers with few romance and comedic moments, while still keeping a violent aspect - do not mistake this series for a light-hearted funny drama either - then this is for you. I must say that the plots and mysteries are really good, from episodes to episodes, as I said we do not get bored and we want more.
It is still enjoyable to watch for those like me, who lean more towards thrillers without romance or comedy, with solid script and realism, you can watch it, it's good.