It is impossible to consider any HP film on its own merits. They will always stand in reference to the books that spawned them as derivative media properties. In this case, the film comes off as a Cliff Notes/ADD (Shiny!) version of the book.
- The Weasley twins' joke shop seems to have taken over the Gringotts Bank space on the Diagon Alley set. The twins speak in unison, which is less amusing than their previous style, but in the rush-rush pace of the movie probably saves a few seconds. A poor trade-off.
- Much of the film has the same washed out, over-exposed color palette and photography that marked Terminator Salvation and bits of Star Trek. I hope this is a fashion that soon passes in Hollywood.
- (I just realized that Twilight had a good bit of this also. As a film, it is really sad that HP6 is closer to Twilight than anything else.)
- JK Rowling invented a huge number of interesting characters, and even the books had a hard time fitting them in. Now even substantial characters such as Neville Longbottom are reduced to cameos. Luna Lovegood comes off much better and has some of the funniest lines and deliveries. (Her name has that James Bond female sidekick quality, is there any Bond/Potter fanfic out there?)
- Rupert Grint and Daniel Radcliffe both have a chance to chew the scenery, which they never had before. The audience greatly enjoyed both. Emma Watson (grrr) had less opportunity to shine, being reduced to crying, hitting Harry over the head and staring into the sunset. Her arch comments of previous films and great talent with magic are sorely missed. I can only hope that the next two films, based on the last book, will give her more space (since Ron Weasley is offstage for a good bit of time).
- Quidditch scenes are handled very well. 'nuf said.
- Helena Bonham Carter, another standout scene chewer as the psychotic Bellatrix Lestrange. She is given screen time instead of the character Rufus Scrimgeour. So the whole political subplot is lost, sadly.
- Alan Rickman has been one of the most reliable actors in the HP stable, but his delivery of the revelatory "I am the half blood Prince." line is a major disappointment. The counterspell to Sectumsempra was also supposed to sound like singing, if I recall the book correctly, but Rickman doesn't come close to that.
- The Muggle waitress in the opening subway sequence was a nice innovation. Just eye candy, but welcome nonetheless. (And yes, there is such a thing as product placement in an HP film!)
The big news, of course, is how different the denouement sequence is from the book. In one sense it is actually better, since it demands that Harry actively trust Dumbledore rather than just being a witness. But it has many other failings, including failing to be the "trash the Hogwarts set" that it should have been. This does not bode well for the final movie. But the real flaming mutual hatred of Harry and Snape does not come to the surface. That will greatly diminish the next films.
With an extra six months from the delayed release date, they could have done a lot. I'm disappointed if all they did was 12 minutes of IMAX 3D work.
The film is state of the art Hollywood, meaning high production values and absolutely formulaic. It will be a hit with its fan base.