As mentioned earlier, my main gripe with the drama was with its pacing issues and repetitive scenarios. The overarching mystery developed a little too slowly and awkwardly for my liking, while the individual cases of the week often felt irrelevant and too heavily padded with fighting scenes. How many times did we get to witness gangster Woong-chul and hitman Tae-soo taking on a whole bunch of thugs (and coming out on top)? How many times did we witness half-hearted attempts on Jung-moon's life? The short answer is that it was more times than necessary, and the amount of repetition took away from the seriousness of the story. It diluted the overall intensity of the story that the show wanted to tell, which was a disappointment because boy was the story intense when it wanted to be (namely when it chose to focus on the overarching mystery).
Much of that intensity in the story owes to the stellar acting performance of Kim Sang-joong as the dogged detective Goo-tak. Sure, the actor wasn't perfect all the way, and there were times that the character came off as bratty and childish (although that may be more of the way the character was written). However, he turned on a powerful and emotional performance when the time called for it, and helped to add many layers of depth to what could have been a potentially one-dimensional character. The eventual reveal and fake-out behind his true motivations kept the story interesting and intriguing as it continued onto its final home stretch, and the show was definitely much better for it.
It was just a pity though that after having such a strong and engaging mystery, the show faltered and mis-stepped in the resolution of its story. The final villain's identity was all too predictable; his downfall too easy and lacking impact. I might even go as far as to say that his "defeat" at the hands of the Crazy Dogs felt campy and contrived. The eventual reveal of Jung-moon's mysterious past also proved to be a let-down as it turned what was a morally ambiguous and grey character into someone that was pure white. In comparison with the rich and well-wrapped up stories of Wong-chul and Tae-soo, Jung-moon's story felt like a huge waste of a potentially terrific conflict.
All in all, it may sound like as if the show had a lot of flaws and that I didn't enjoy watching it, but you do tend to expect more out of a story that is brimming with potential at its onset. Bad Guys' inability to ultimately fulfil that potential only served to detract against itself. However, that certainly didn't stop it from being an entertaining watch.
