This review from the Guardian is correct in a big picture sense, although not enitrely correct in the details.
One thing that is obvious if you've seen a Harry Potter film without first reading the book is that there are plot details you are unlikely to notice, or which you may not understand, until after you read the book. This can significantly detract from viewer experience, to the point that many people I know who have not read the books wrote off the films after one or two installments. At one extreme you have Roger Ebert's shock that Harry Potter films are getting darker ("My hope, as we plow onward through "Potters" Nos. 6-7, is that the series will not grow darker still." Er... don't hold your breath, Roger.) But at another extreme you have observations like this,
But, yes, here is the film where Potter gets some serious romance, with fellow Hogwarts scholar Cho Chang, played by Katie Leung - though bafflingly, and rather ungallantly, her character is completely dumped from the action after the snog....If you pay close attention to the film, you understand the cold shoulder (and even see some regret), but if you've read the book you know exactly what happened. This isn't Kubrick's 2001, A Space Oddysey or Peter Brook's Lord of the Flies, but it is a situation where you will almost certainly enjoy the film considerably more if you have read the books.
Although the critics don't seem to agree, in many senses this is the best film in the series. Despite the fact that this was, at least in my opinion, the most difficult book of the series to adapt to the screen, the script and pacing are better than some of the prior films, the young protagonists are more capable actors in each successive film, there's a good sense of "time and place" - of a world apart from our own, and the British character actors who play the teachers and villains continue to provide amusement. The reviewer writes,
The Harry Potter series has become famous, or faintly notorious, for giving work to almost every single British character actor in the Spotlight casting directory, with the exception of Stephen Fry, and he surely is lined up for something in the future.Actually, he was a narrator in the fourth film, so perhaps they've already run out? Fortunately not, and it can be a treat seeing actors like Robert Hardy pop up in these films, or how well actors like Alan Rickman and Imelda Staunton can take ownership of Rowling's characters.
The film which appears to be the favorite of critics, the third in the series, was also the least faithful to Rowling's vision, with the critics describing that as a positive. Yates seems to have a respect for Rowling's vision more kin to that of Chris Columbus, but with a greater aptitude for filmmaking than was evident in the first two films. Many elements of the novel which seemed as if they would appear silly on the big screen are translated quite well, or are gently adapted to be both true to the original story and (beyond the necessary suspension of disbelief) credible. While the last two directors have quietly stepped aside after a single film, I can't say that I'm surprised that Yates was again picked to direct next year's installment.
The reviewer comments that there seems to be a lack of "development from film to film":
As I say, that's a relief, on balance. But every time I sit down to a new Harry Potter movie, I'm struck by how very, very similar it is to the previous one - and how forgettable, even disposable, the plot twists are.Approaching these films as action fantasies or spectacles, that's no big deal. Who cares if there is development in the character of James Bond or John McClane? (Who would even expect it in a Jack Bauer?) But if the series is to truly offer more than a series of fungible thrills, it's up to Rowling in her final book to provide what she has at times promised - a conclusion which ties together elements from the prior novels that readers might have previously thought irrelevant or peripheral to the plot.