I think Harry Potter and the Order of the Pheonix was the best book yet, even though it DID have its flaws.
I think Rowling could have made the body of the book a little more interesting. I mean, the most exciting part was obviously the part at the Department of Mysteries where Harry, Ron, Neville, Hermione, Ginny, and Luna fought the Death Eaters. During the school year all that basically went on was that Umbridge woman banning Harry from basically everything and Harry having those visions or dreams or whatever you want to call them. I think Mrs. Rowling could have made something more exciting happen with the Order during the school year. I waited for the 5th book for 3 years because I was dying to find out what happened with Voldemort, and the only big part with Voldemort was at the end of 800 pages of detentions and punishments and dreams. Not that those things weren't exciting. I found the book very enjoyable to read and I can't wait to read whatever Mrs. Rowling has got in store for us muggles next.