It's really addictive! If you like dark mature dramas with grey heroes that aren't really good or evil (and some bromance), you'll probably really enjoy this. There isn't any romance :)
Of course it's personal preference (and I respect that!), but I don't know why so many people ship Dam and Sun Woo, I experience second male lead syndrome quite often, but he just annoys me. Like pls stop interrupting Dam and Woo Yeo's relationship T__T