I love the Harry Potter books. I also love A.S. Byatt's Possession: A Romance (whose near final installment of his novel [b:The Old Curiosity Shop|429024|The Old Curiosity Shop (Penguin Classics)|Charles Dickens|http://ecx.images-amazon.com/images/I/51CrLM5XtJL._SL75_.jpg|1098758] was greeted as it arrived by steamship into the New York harbor by a cry of "Does Little Nell die?").Harry Potter and the Order of the Phoenix
isn't perfect. As each successive book has increased in size and scope, Rowling has more and more trouble keeping the same smooth flow that characterized the first couple of books. While the focus never truly strays from Potter in any of the books, the slow accumulation of characters means that Potter's necessary interactions increase exponentially. So, in this book, we get to see what's become of Prof. Lockhart, the ongoing Percy Weasley vs. his family thread, more revelations for Hagrid, Neville Longbottom, and Snape, etc. Each character demands his or her ten pages and if that means that a 300 page book bloats up to nearly 900, the fans aren't complaining because they find these side trips as fascinating as the main road.
As a complete work, the Potter series will not rival the structural beauty of something like Lord of the Rings or even C.S. Lewis' "Narnia" books. Tolkien didn't release his work an installment at a time, and while Lewis did publish on the installment plan, he didn't continue the same characters between the books. But just because Rowling isn't like these previous authors doesn't mean that her work is less good, or that it will be forgotten in fifty years. I reserve judgment on that until I've read the end, which is now only two books away.