This work is fantastic, but I won't exactly give it a full 10/10 because I'm judging this based in two different ways. After reading a few of the ratings, I want to voice my opinion on this work as to why its an important read and how it should be thought of as you read it.
As a manga its wonderful, the character growth and developments are fantastic. The plot development and ending is a little lackluster for a manga which is why I don't exactly give this a full score, but that doesn't mean it isn't an amazing work! Ooima chose to use manga as her medium for this work and I think its an appropriate choice based on the way the message being conveyed. Its tough to get the same emotions coming out if you publish this as a novel with just text, however if it was published as a movie I feel that the time constrictions it cannot do the character growth any justice. The length and pacing for this was perfect, nothing too drawn out or unnecessary and all of the changes happen naturally for the story's progression.
As a form of literature, this work deserves a full points. The message and theme the work has is powerful and it really reaches out to you. One of my English teachers in high school told me that literature is something that has a message or comment on society, and tells that through the work. Koe no Katachi is a comment on society much in the way novels like "To Kill a Mockingbird" and "The Grapes of Wrath" are, which is why I truly believe this should be considered a work of literature, and should be read as such. What this series does that I love the most is the way Ooima portrays her characters.The characters all have their flaws which allows us to be more empathetic with them. Everyone's personalities and circumstances aren't believable, no doubt, but I think the author made the characters that way intentionally as a way to strengthen the effect of each character's actions. Take Nishino and Ueno as an example. Nishino is the perfect sweethart, very innocent and super caring, all of the bullying done to her by Ueno, unsympathetic at all towards Nishino's plight, is magnified in our eyes forcing us to feel for Nishino. Its this type of characterization that makes the work as powerful as it is, but further amplified by the developments each relevant character has.
I love this work, easily one of my top series.