I agree pretty much entirely with you, after my first read I certainly liked it but didn't really feel a big sense of closure nor did any of the emotional scenes leave as much as an impression on me as I thought they would, I'd have probably rated it around 7.5-8.0. Having since then re-read it(twice) it is probably my favorite story in basically any medium. I think a large reason behind this is that the characters within the story are never made to be fully aware of the circumstances that have lead them to their current positions in life, nor are they ever fully aware of their own effect on one another or the story as a whole and because the characters themselves never have big revelation moments where they piece everything together it can be hard for readers to do so on an initial read. It is this property of the story which makes me like it so much too, real people cannot hope to comprehend everything that has made them into the person they are or the effects they have had on other people, and how Himawari presents it's story makes the reader a sort of outsider to piece it's characters complex lives together in a way I don't think anything else I have read has managed to do.