I read the book two weeks ago and have just viewed the Criterion Collection DVD. I found the book to be complex, rich, insightful, puzzling, and surreal. I loved it. This film comes as close as any film could to the spirit of the novel and still be under 3 hours long.
Oskar is born to three parents who, like the Gdansk they live in, represent 3 ethnic groups: Pole, Kashubian, and German. He is fully conscious at birth and is presented with two paths for his life - one as a shopkeeper and one as a musician. While the people of 1930's Gdansk/Danzig feel forced to choose ethnic sides and mundane occupations, Oskar rejects the "stupid" adult world. He stops growing and learns to assert some control over adults through his drumming and vocal talents.
One of my favorite sections of the book is when he musically subverts a large Nazi rally. Not only was this well done in the movie but was worked into a bonus feature that had Grass reading the book chapter while we watch the corresponding section of the film. The words of the spoken German as well as the subtitled English translation have a lot of power and poetry - this feature is a very rare treat.
You also experience in the film something Schlöndorff confirms in interviews: it is hard to imagine this film existing without David Bennent. His voice and eyes carry so much of this film. The short interview feature with Bennent is delightful.
I thought the bonus feature on the Oklahoma censorship was interesting and somewhat balanced in that it portrayed the zealousness on both sides. However, I would have preferred to see more of Grass or material on the creative efforts of the film.
On a more serious note, I find Oskar's indictment of society very compelling. Something about the way the film brings themes to life (more than the book) makes 1939 Germany frightenly parallel to the US of 2004. In Oskar's world, the people in power make false claims in order to invade other countries, human rights abuses increase and all objections are shouted away with "patriotic" speeches and political rallys. For the most part people remain ignorant or apathetic to the suffering their government officials are causing. (Perhaps we need a few Oskars drumming at the democratic and republican conventions this summer.)
The film stands very well on its own but I would encourage people to read the book first. The book is more complex, covers more years of Oskar's life and it develops some important ideas that are not at first obvious in the film. For example, as Oskar ages he still looks 3 years old and he consciously exploits this by manipulating the adults around him by behaving more childish than he really is. There is also an interesting theme in the book related to Rasputin and Goethe.
It is also worthwhile to do a little browsing on the web for historical material related to Gdansk/Danzig, Kashubia and the large population resettlements after wars in this area. The excellent bonus features also explore the themes of the film and add a lot of value.