One of the most classic forms of the Young Adult novel — predating the current Young Adult publishing boom by decades — is the diary novel. From Judy Blume's Are You There God? It's Me, Margaret through the Diary of a Wimpy Kid series, diary novels have been some of the most successful entries in the Young Adult genre, proving both high-selling and culturally enduring.
Diary novels have a direct appeal to the reader, since they satisfy a young person's urge to read something written from their own point of view. This is especially significant for an adolescent, who is trying to navigate a confusing world as she is growing up and finally starting to see things through her own eyes, not her parents', teachers', or siblings'.
And indeed, diary novels are often written from the perspective of either pre-teens or early adolescents, since they capture that moment when not just our protagonists are changing, but all their friends and classmates are changing too. Are You There God? It's Me, Margaret is a classic of the genre and portrays a young girl who is going through puberty. Published in 1970, it came at a time when sex education and conversations about a young woman's body were not available to every young girl going through puberty. The book was powerful because it gave young women a way to see depicted an experience they universally shared through an intimate perspective.
While it's not a work of fiction, The Diary of Anne Frank has enjoyed similar lasting power because it shows us the ordinary struggle of being a young teenage girl combined with extra-ordinary terror of being a Jew in hiding in Nazi-occupied territory. Anne Frank's diaries stand as such an important historical document partly because the book gives us a perspective we can easily identify with to portray an experience that is so foreign and horrific to the average reader who only knows about the Holocaust through school and more conventional history books.
So, when Jeff Kinney says in interviews that he's just trying to write a fun novel that will get kids exciting about reading, he's underselling the appeal of his own books a little bit. A big part of what makes Diary of a Wimpy Kid so vital to its young readers is that same aspect that makes the diary such an enduring form in the Young Adult genre. Kinney shows us the perspective of a middle school boy living in this day and age. He's obsessed with video games, but he also likes Home Economics. He's kind of embarrassed by and sometimes resentful of his friends, but misses them terribly when they're not around.
When Greg makes a joke we laugh with him, and when he gets bad gifts at Christmas, we recognize that as a Christmas we've definitely had. That's why it doesn't matter so much if Greg is a good kid or a bad kid. Young readers recognize that middle school is confusing and you might do the wrong thing a lot of the time. The power of the book is that it just shows a kid living his life—warts and all—which is something so few other novels make so hilarious.