My wife asked if it was "true to the book" and I told her there was no such thing as "true to the book." You've got the radio series, the books, the TV series, the adventure game, and now the movie. They're all different. There is no such thing as continuity in the Douglas Adams universe, there is only what seems to be the funniest choice at the moment.
And often, to its credit, the movie did the right thing. The whale scene was absolutely perfect. Marvin was a great character, delivering everything I would have expected. The other computer personalities were great too -- the sighing doors were funny and Eddie the computer was dead-on (although they left out his "Jewish mother" personality, no big deal). Slartibartfast struck the right note, and the scene with the planet construction warehouse was just awe-inspiring, and I think it did justice to Douglas Adams' likely vision of what it should have been like. And to be honest, the scene where Marvin shoots at the Vogons with the point of view gun -- a scene which was not in any of the other versions as far as I know -- was hilarious.
So the movie was "good enough". There was not anything I saw that was really, seriously wrong with it. Having said that, there were very many things in the movie that just seemed like uninspired choices, as in "They're free to go with their artistic instincts, but I'm not sure I would have done it that way."
For instance, the romance between Arthur and Trillian? I don't feel that it was anathema to the books, but it was just a waste of time. Arthur really did like Trillian a lot, enough to challenge the god Thor to a fistfight in book three, and I think they spent some quality time together near the end of that book, though I'm pretty sure they never slept together.
But I suspect that Douglas Adams wouldn't have given that much credibility to sappy emotional scenes. The theme of his books is, "These characters are all alone in a vast uncaring universe, and they're trying to do things that will make their lives mean something, and that's just so pathetic that it's funny." Hence, the whole scene where Arthur whines "The only question that matters is, is she the one?" just seemed out of place in the story, even though it was just the setup to another joke. Plus, you know, she's actually NOT the one, since Arthur falls in love with (and loses) Fenchurch later in the series.
Then there was the scene with Humma Kavula (John Malkovich). Amusing. Gave them an opportunity to use some keen looking special effects. But just not necessary. As far as I can tell, the entire point of having Humma Kavula at all was to set up the punchline of the movie. Humma tells Zaphod to find the point of view gun, and that winds up in Marvin's hands, and Marvin shoots the Vogons. And like I said before, that was really funny. But I'm not sure it was funny ENOUGH to justify the set-up to the joke. Also, I don't really understand what Zaphod's reason was for wanting to visit Humma in the first place. Just so he could tell him "Don't call me stupid"?
Then of course there's Zaphod himself. Okay, so they did something different with his two heads. Could have been worse. But for the first half of the movie, the personality was right. He was the right combination of arrogant, dim-witted, lovable, and nuts. Then for some reason that I just don't understand, they took away his personality in the second half and basically wasted his character for the rest of the movie. Why? I just don't get why they would take one of the best characters and throw him away.
So, what worked:
- Marvin. DEFINITELY Marvin.
- The Guide.
- The whale.
- Zaphod during the first half.
- Marvin shooting the Vogons.
- Planet construction.
- The shipboard computer.
- Zaphod during the second half.
- The emphasis given to Arthur and Trillian's romance.
- The improbability drive.
- Humma Kavula.
- The mice.
- The dolphin song.
- The Nutrimat making the substance that is "almost but not quite entirely unlike tea."
Final score: *** out of 5.