What I think where they are strongest is the sense of complexity. There is a level on which these could be straightforward - the stories of a girl losing a best friend, or of a girl leaving foster care, or of being a twin. But Wilson does a nice job of layering other things on top of it, making the lives of her characters complicated in ways that feel very much more life.
So in this one, Jade suffers the lost of her best friend. But it isn't just a take on her grieving. Her parents are kind of jerks, at times, and have their own stuff going on. Her dead best friend's parents are similarly wrapped up in their own pain. Other kids at school have varying reactions to Jade as she negotiates her Vicky-less world.
Vicky runs out in front of a car after school one day, and is hit. She dies later that day. Her best friend, Jade, who long hid in Vicky's shadow, is suddenly without her rock. Her parents are less than helpful, telling her talking about it and asking for help are forms of weakness. (Although they may be saying so to cover that they can't pay for therapy, and are afraid others might say they aren't good parents.)
Jade joins the Fun Run club, which Vicky was convincing her to join right before she died, and stays away from the Drama Club, which is what she really wants to do. Vicky not only overshadows this book as an absence, she's an active character. Vicky's ghost, or at least, Jade's projection of one, hangs around Jade. (The book doesn't definitively come down on whether or not this is supernatural.) We get the feeling that Vicky wasn't always a particularly nice person, or at least, Jade's memory of her seems that way. How do we deal with the warts on people we love who have died?
This is what I think makes these books more than they could be. The complexity stands up nicely to the very simple prose, and balancing the two is by no means an easy task. But all the same, I can't say I love these books. I know they're obviously greatly loved by the BBC's reading public, since there are so many on the top list, and I get why childhood favourites are disproportionately represented there. Still, it feels like something's missing.
I don't know what it is. But this are interesting books, and for children struggling with difficult times, I think they're good enough not to be insulting. There's nothing worse than saccharine reassurances that everything will be fine. These books manage to come to reasonably happy endings without feeling like they're faking it.
Read as part of the BBC Big Read