Note: I watched it at the Toho Cinema Complex in Ario Nishiarai (*I had thought I could have been the only person on this review list who had really watched it at a cinema in Japan after reading a particularly harsh review, but I was wrong).
A quick overview: Koe no Katachi is a very well done film, although not without shortcomings, and which has dealt with (a) complex issue(s), and which leaves the viewer with questions but no easy conclusions. It is a powerful enough film to remember and ponder over, and people may draw different lessons, or perhaps none.
Pros: The sound and vision (KnK is top-notch Japanimation. I dare say that in some aspects, it is better than a Ghibli film). The ambient piano background music really matches with parts of the film, and the use of marimbas and even silence at the dramatic climax worked out well. Shoko Nishimiya is adorable when she has that half-proud and half-shy face when she does ponytail. Cute, but elegantly done and not unpleasant. However, was this better than Tamako Loves Story - I cannot tell. There were recognizably magical rooftop sequences in Yamada's K-On! and at the classroom and school ground with Midori in Tamako Love Story. I am not sure whether KnK had such "magic" moment despite its very fluid art.
Voice actors have all done a great job. Saori Hayami, Yuki Aoi, Miyu Irino were expectedly good, and Kaneko Yuki (who played Midori in Tamako) was a great pick for Ueno, another difficult character.
Con: I feel that the original manga's theme was very challenging for a very young manga artist to deal with; I also felt that some themes weren't fully explored or developed properly. Besides the bullying/redemption theme, there is an attachment/detachment in relationship theme, and on top of that, a male-female friendship and romance theme. Those themes coexisted and had resonated against each other for sure, but it's not done in a well-calculated and clear-cut way. That was the main issue of the serial manga, and to explore those themes, the manga author had to involve the characters to comes to terms with each other in a slightly forced situation (like the movie club and the event of going to a theme park).
Although the story line of the movie club was completely cut and altered, the theme park sequence was saved for the film- which still felt forced. However, I felt that Reiko Yoshida has done a nearly perfect job with script-writing and editing the story to be able to fit in for a two hours film. My only grievance is that the reason behind Nishimiya's decision at the climax was not convincingly told (which was as in the manga- but the Manga fully told Shoko's mother's sufferings of being divorced because of her child's disabilities and sis Yuzuru's side story of being bullied because of the same reason- so there was a more natural reason why Shoko should have cumulative feeling of guilt that she was making other people involved with her unhappy [and not just that sense of guilt towards breaking up Shoya's relationship with others]). Viewers might be puzzled then why Shoko had to make that decision in the climax (as it was already not exactly written convincingly to start with in the original manga).
Final verdict: Having written down the cons, this is a very challenging work of art (yes, "art", which is not simple "entertainment"), and it did choke my heart at several moments. This won't be everyone's favorite, as it deals with a serious and dark issue, and as it's not all straightforward (as in Tamako Love Story) - but it leaves viewers questioning about their own relationship with other people in the past and present.