I read "Ann of Green Gables" about a year ago. Of all the books I have ever read, this one had one unique element--more on that later.
The basic story is simple. An elderly couple (brother and sister) need help on their farm and decide to adopt a young boy. Instead of a boy, a mix-up leaves them with a girl. Though the brother takes to her immediately, the sister takes more time. The girl is a dreamer and loves gothic stories of tragedy and love. Whatever she does, she does wholeheartedly.
As the girl grows older, she, naturally, begins to mellow. By the end, she is an adult who has put many of her childish fancies aside.
This brings us to the unique element. In the beginning of the book, it is not only Ann who is over-the-top in everything. The author's voice is as well. All the descriptions are enthusiastic and a little overblown. If the book continued that way, it would have been cloying and annoying. But by the end of the book, the author's voice has also mellowed, the storytelling has become more settled and mature.
I don't think I have ever read any other book in which the author's voice changes and matures as the book progresses. That makes this book unique.
I don't think this book is for the middle grades, but junior high and up would enjoy it.