The best thing about this drama is the acting, it's very good in general and Nam Joo Hyuk does a very good job as main character. I did also enjoy some of the music, it was certainly more up my alley. That's all for me.

Contrary to other people I didn't think this drama was fast paced, in fact I thought it was slow, going in circles sometimes, and I got bored at times and found myself doing other things while watching. The plot is quite cliché in my opinion and except for maybe around three characters the rest were very one-dimensional, especially the bad guys. We don't learn much about anyone anyway, so it's quite superficial and it didn't make me connect with any of them, not even the ML. I also liked Choi Mi Ryeo and Cho Kang Ok as characters but I so wish we had gotten so much more insight into them, I didn't learn much at all about them. The dynamics of ML with his classmates could have also been deeper, but because it wasn't what happened in the end of the drama made me feel nothing. It felt even the writers/director knew this though, because it's treated as very secondary, something that happened in the background.

I'm ok with anti-hero stories, I do generally prefer them over hero ones, but it's not new nor fresh, and cases of corruption at all levels have been done many times as well. I don't think this drama brings that much new to the table that wasn't there, so I was not awed by it and I thought it was average. It's still watchable, especially if you like action thrillers, but it's not a masterpiece by any means.
Echoing what another user said, the fighting choreography was not bad but the way it was filmed adds no tension and didn't do any favours to the overall fighting dynamics, at times I felt I was missing the good bits, camera in and out... quite chaotic in my opinion.
I don't think they achieve enough in terms of discourse, there isn't any depth in the corruption itself either, nor in its politics, or the police involvement. Obviously there is no real debate about the police as an institution, despite the ML being both in and out of it. I haven't read the original material and it makes me wonder if there was a lot more of that that was cut out of the story.

Recommended to those that like action thrillers, it's entertaining enough but keep your expectations low to mid level.