Feels like the director and actors don't really understand the characters to that extent.
Small details that could tell a lot about the characters but does not show in the movie, for example, Violet wore her sister's glasses as her way to remember Eleanor but after being rescued by Finch she was no longer stuck with those, or how Finch cannot bring himself to say the f word at first but finally freed from that, or how Finch was affected by the bird when he was a kid (his symbol in the book by the way), which changed his view toward life a lot.
Not to mention the lack of Finch's father role, which to me is the key fact that led Finch to his state, while I'm rather accepted the missing part of his mother and his small little sister as well as the "Roaman" in the movie.
Drone on, the part when Violet started to find "what left of Theodore Finch" as she was finishing their project is what I find really inspiring from the book, that is, showing the raw truth of life when people lost a person they love, was not shown in the movie, which is quite disappointed to be honest.
The movie was not up to my expectation, but if anyone find the movie good and want to understand more about the characters then I really recommend you guys to read the book. It helps you have a deeper look into each and every of them in a more fulfilled way.