When I read this book, I was very glad that J.K. Rowling again didn't disappoint the fans. Though the magical world described is highly unnatural, Rowling excels in making the characters, events, items and so on look very natural indeed. What I particularly liked about this book, compared to the other books, is the real clash of good against bad. Of course it has also been like this in the other books, but for the first time the entire magical world has to choose a side. And it's not just Harry and his friends who fight Voldemort this time, but there is an entire movement, which fights Voldemort and his Death Eaters.
I am not 100% positive on the book, because I feel that this book is too much a bridge for book no. 6 or perhaps even the seventh book. The real clash has so far been avoided in this book. I also feel that this book, just because of what I just said, doesn't reach the heights "Harry Potter & The Goblet of Fire" did.
I must compliment Rowling on making the characters much more interesting and for letting them develop. It's good to see how Neville is growing in the books. And it is also good to see that Harry suffers some losses. He is no longer that nice, heroic guy; I actually found myself starting to hate Harry in this book. It goes to show that nobody is perfect.
I would love to see more of the Death Eaters (they're much more fascinating than Voldemort himself), of Cho Chang and most of all, of Hermione Granger in the next books. She is for me, the nicest and best character in the books (followed by Professor Minerva McGonagall). Bring on number six, please!