I'm giving a high rating because I enjoyed the drama, but I still feel like something was missing.

The beginning of 'I hear your voice' was promising - to me, it seemed like the writers will pay more attention to the trials and the law part of the drama. And since I am a big fan of law dramas, i got excited. Too excited. Everything was okay, the pacing was normal, the stroyline was getting better and the characters were funny. And then, somewhere in the middle, it felt like the drama lost its spark. Not completely, there were exciting and thrilling moments, but it became too messy so it was easy for me to get annoyed and bored. The part that frustrated me the most was when the writers dropped the amnesia thing out of the blue. (I hope this is not a spoiler since there is an amnesia tag everyone can see) Seriously, it was unnecessary. I still don't understand the point of this amnesia.
The characters were the reason why I didn't give up on this drama, I loved every one of them. But if I have to say who's my favourite one, I'd say Kwan Woo. Seriously, Yoon Sang Hyun never disappoints with his roles. I don't know how, but he always chose the best fit for him, so I always end up loving his character. I loved every side character, I'm not joking. Every one of them. It's usually really rare for me to like every character, without having at least one that annoyed me. I couldn't even bring myself to hate the criminal despite all the people he murdered. He was cruel, but the people who made him like that... Yes, they were also cruel. There's no much to say about the two leads, Hye Sung developed a lot so that was a plus for her. Jong Suk's character was... not different from his other roles? Still, I liked Soo Ha. Another plus is that they didn't make Do Yeon a heartless bitch, she is maybe my second favourite character.
The ending was okay, but too predictable. Maybe the part I enjoyed the most was Dal Jung's trial.

The acting was good, no much to say. Kudos to Jung Woong In for his good portraying of the murderer.

Most of the OSTs songs weren't something special, but since they suits the drama well, I liked them.

I'm not sure if I'll rewatch this, but I will miss the characters, so who knows.

Overall, I'm giving an 8 mostly because of the characters. I'm not saying that the plot was bad or something, just i wish it would have been better.
Anyway, the drama teaches you that telling the truth is always the best option. It also makes you wonder if reading people's minds is actually a good idea. There are many good parts of it, so I recommend it no matter what genres you like.