If there's anything this movie proves, it is the difficulty in separating the series from the demands of fans. This is clear just from hearing some of the comments. "Why didn't they identify the names on the Marauder's Map?" "Why wasn't the second Quidditch game shown?" "Why wasn't there more of Crookshanks the Cat?" By focusing on what the film didn't have, fans fail to look at the film on its own terms. I think this is by far the best Harry Potter movie yet.
The only way to satisfy fans would be to include everything from the book, which would require a miniseries. Since that isn't what these films are, the story has to be abridged. The first two films tried to fit everything they could within a reasonable slot of time. The result was a set of films that felt cluttered yet incomplete. Had they continued with this strategy for this movie, based on a much longer book, it would surely have been over three hours long.
The virtue of the latest film is that it makes a real attempt to adapt the story, not just marching in lockstep with the book's events. The screenplay is sparing, leaving out or simplifying loads of details not directly relevant to the plot. But it captures much of the book's delight and humor. The first two films fell short in this regard, because they lacked the guts to tinker with the details, even though that was the key to condensing the story while staying true to its spirit.
The movie is still faithful to the book, of course. Many of the scenes are exactly as I had imagined them. When it deviates, it does so based on an understanding of the story and characters. This is evident in the way they show, for example, the Knight Bus; Hermione's overstuffed schedule; and the introduction of the Marauder's Map, a scene that captures the twins' mischievous personalities. The changes are clever and funny, and they help compensate for the movie's loss in other areas.
Certainly this has something to do with the new director. Columbus's approach was to stick to the books as literally as possible, often draining them of their subtlety. For instance, where the books only hint that Dumbledore can see through the invisibility cloak, the earlier movies make it unmistakable. The new director never condescends to the audience in that way. This is a children's movie, but it is also a fantasy-thriller that we can take seriously, because not everything is spelled out for us. We're given a chance to think.
But part of what makes the movie work is the book itself. The story is gripping from start to finish, because the threat looming over the school is established early on. Harry's personal life is sharply intertwined with the plot. We feel for him as we watch his disastrous (but hilarious) attempts to escape his uncle and aunt, and his humiliating reaction to the dementors. The story avoids common devices such as the talking killer or deus ex machina, which the other books have in abundance. The ending is nicely bittersweet and ambiguous. The plot is so complicated, however, that the book spends several chapters explaining it all. The movie wisely includes only very little of this, allowing the plot twists to become understood as the story progresses. I was surprised to see certain events that were in the movie but not the book lend support to an important theory some fans have had about what is to be revealed at the end of the series. Of course, it is well-hidden and won't give anything away for those who aren't looking for the clues.
I was so satisfied with the film that it almost seems trivial to mention the flaws, but there are some. The portrayal of Fudge's assistant as the standard hunchbacked dimwit is out of place here, as it would be in anything other than a cartoon or spoof. The most serious misstep, though, is the casting of Michael Gambon as Dumbledore. Gambon's face seems frozen in a perpetual nonexpression, and his voice lacks resonance. He compares poorly to the late Richard Harris, whose line readings had gravity, and who played the character with a twinkle in his eyes. It is a pure mystery to me why this actor was chosen as a replacement, especially considering the fine performances from other members of the cast. Even the children are in top form here.
Those complaints aside, this is the movie I was hoping they would make when the series began. If it doesn't live up to the book, so what? What's important is that it lives up to its potential as a movie. Fans who want a carbon-copy of the book are looking in the wrong place, because they're never going to get it here. This is probably the best example of a Harry Potter movie that we're ever likely to see.