The first episode was absolutely gut wrenching. I was not prepared for that.
Please note that it is quite violent and it also contains child abuse etc.
Some episodes left me with a bad feeling in my gut.

The story is great and it has a good plot. The music is on point and they don't drag out unnecessarily.

However, if I have to rate Ms. Kang. Wow, please someone shoot me already.
First of all, she's a cop, but she absolutely does not behave like one.
Cops are supposed to be trained, right? Well you'll question if she had training as a cop at all as she is vulnerable asf and she fends herself like an 80 year old ahjumma. This is my first annoyance.
Secondly, voice is pretty much about her ability to hear and her quest to find murderers.
Except... Every time she hears ANYTHING at all she just decides to stand there like an absolute babboon and wait half an episode (just kidding but at least 5 minutes) before taking action. Half of the time she just says "I think I hear something". No sheit bro, that's the whole point of the show???
*someone gets murdered or attacked in the next room* Her ability to hear more gets yet another eye catcher. "I hear something" She hears signs of a struggle: "I think I hear something". If I see smoke in the hallway, i'm not going to sit around and smell the air and wait until the whole building is on fire to then casually say "I think I smell smoke".

Moo Jin-Hyuk, played by Jang Hyuk, is a very good actor and very suited to play an angry and motivated by vengeance detective.