Yeah, I was disappointed as well. Rated it as high as a 6 though. There's some interesting psychology in it. For example, although never stated, I believe the Naoko character is explained by being desperate for family. That is why as soon as she gets to know someone, she loses romantic love and converts them to virtual brothers.
There are other things going on with Reiko and Midori that are interesting to think about as well.
From all accounts the novel is much better though!