I read the eight Anne books when I was about 14 years old, and I remember that I enjoyed the first three books, but lost interest somewhat after that.
I am now reading through these books again as an adult, and now I see why I lost interest back then after the third book--because Anne of Windy Poplars is sort of just a "filler" book.
The first three books are really excellent. In them we get to see Anne growing up into a mature young woman, and eventually becoming engaged to Gilbert Blythe. After reading those books, most people will want to see what happens when Anne and Gilbert start their life together--these people should continue on to book #5, Anne's House of Dreams, where the story continues.
In book #4, Anne of Windy Poplars, nothing important happens at all. (This is understandable, as the author wrote this book much later than the other books, just to fill in some missing years.) Rather, we witness a series of adventures and triumphs that Anne has while working as a highschool principal in the town of Summerside, for three years while Gilbert is finishing medical school. Much of Anne's adventures here involve acting as a matchmaker for the town's various residents. She meets many interesting an eccentric people in Summerside, and although there is one tragedy, most of the book has a very light tone.
As an Anne lover, I did enjoy this book. It is not as compelling as the earlier books; and quite frankly, it annoyed me that Marilla, Diana, Mrs. Lynde, and the others from Avonlea are barely mentioned at all, let alone appear in the story. Also it irked me a bit that about half of the chapters are in the form of letters from Anne to Gilbert, but we never see a single letter from Gilbert! But, I can't seem to dislike anything L.M. Montgomery wrote. This book, like all her books, reminds me of a rambling stroll down a quiet country lane. Very little excitement or danger. No sex or violence. But lots of amusing conversations, lovely descriptions, interesting characters, comical situations, and above all, the feeling that I am escaping into another time and place--a gentler, more simple time, and a beautiful place.
So I give Anne of Windy Poplars 4 stars, and I recommend it for those who love the Anne books, although more casual readers will want to skip it and move on to Anne's House of Dreams.