Well, this is the story of Hwang Dong Joo whose father was involved in a massive financial scandal and whose circumstances of his death remain suspicious. Hwang Dong Joo becomes a chief of taxation at the National Tax Service. He works hard to achieve his purpose and revenge.

Now the comments are mixed on this series in general and contain only two reviews. I want to say I thought it was a thriller as the tag meant but it was more of a drama overall.
So, I had to give up on the thriller atmosphere that I love in general, and although here it was more colorful and light-hearted, there was enough action and thrilling moments to keep me focused.
The series has its somewhat silly and clichéd sides, where Hwang Dong Joo is a step-ahead of everyone else, the false suspense when you're supposed to believe the antagonists are winning, the slow-motion moments a bit cheesy. Well, if we forget that which is inevitably part of Korean dramas, the series is very enjoyable.

Hwang Dong Joo, despite the fact that it is predictable that he often wins, I like his character, he is a smart-ass and moreover arrogant and frank, a little rough but funny. Honestly, a kind of arrogant character that we love because he says out loud what the viewers are thinking quietly, especially to the antagonists. So his character is really enjoyable and a treat for us.
I have to say that the other characters all pretty much have a clichéd role in traditional k-drama fashion. The somewhat dumb but big-hearted teammates, the sometimes annoying superiors and the subordinates who are assholes, the "evil" director, Seo Hye Young (the FL) who is generous and friendly but sometimes a little dumb, and then the mentor who can be trusted.
In short, a quite few clichés, and I would have liked to see more complexity in the characters.

As for the plot and the story, I must say that it's pretty good overall, we have several cases that come together and that lead to the grand finale and to put the antagonists in sight, the words are certainly technical and the meetings quite incomprehensible for us who have no knowledge of how these finance companies work but it is quite easy to follow overall. We follow Hwang Dong Joo with delight in his revenge and taking down the antagonists who are really too arrogant for their own good. The story is really about revenge with a sassy but fun character who is determined to bring down the entire system if need be. There is a lot of fiction, but also quite emotional moments, honestly this drama gives us a bit of everything, and it's very well done.

I would like to add that there are a lot of series produced in South Korea that I could qualify as made in "k-drama fashion" so comedy, silly, emotional and simple, sometimes bad acting.
This series although not hugely elaborate, should be the kind of standard for the industry, this is what a k-drama should look like, not low-end series especially in acting and script. Frankly, this series is solid for its genre.

So, I would honestly say to at least see the series because Hwang Dong Joo is worth it as a character, it's really him who carries the series and makes us want to follow his adventures, certainly it's not ground-breaking but his character is worth it, and like I said, it's pretty solid.
With that, I'm going to get into season 2 right now.

Ps. It's been hard to get good subs for this series which is a shame because it deserves to be commissioned properly, I believe Kocowa did it recently but only for the American continent and in addition the season 1. So I recommend the links shared by Tax Payers Sub Team who did a superb job to sub this series for international fans and the entire two seasons.