This is the first time I have tackled Anne Frank, as there is a bittersweet notion to this story when you consider how it ends. It is especially tragic when you realise that Anne and her family, along with four others, lived reasonably normal lives for two years in their secret home in her father's warehouse. Also, the fact that their lives ended so close to the close of the war makes it even more poignant.
Anne Frank, who had dreams of becoming a writer, shows that she has a great skill for it. Even the most mundane activities become interesting with her telling, and the fact that she could keep her story interesting throughout this work when her family never once went outside their hiding place is a testament to her talent.
While the book begins with her as a moody teenager, over the course of her story, it becomes clear she is maturing. She still has fits of moodiness, of course, but considering her life is at risk, requiring her to live inside and hidden from the world around her, it's no surprise she was moody and depressed. Surviving in such a situation for so long would take a lot of strength.
This may be officially for young readers but if you haven't tried Anne Frank's story yet, this may be a good place for you to start.