Don't Panic!
(I was planning on posting this on the 16th, but I didn't. So here it is now.)The Hitchhiker's Guide to the Galaxy is a movie that is almost, but not quite, entirely unlike the material upon which it is based. This is not a bad thing for two reasons. First, a literal translation of the novels or radio series to film would simply not work. Both sources are too tangential, a tad aimless, and undeniably British, and these are qualities that work counter to the format of North American cinema. Second, every fan of the Hitchhiker's Guide already has a version of the film in their heads, and trying to outdo that version would simply fail--this is true of any adaptation anywhere.
With that in mind, (ie. knowing that what you will see in the theaters will not be expected) you would do well to go see the Hitchhiker's Guide to the Galaxy right quick, since it happens to be a very good movie. It both contains all the essential bits of the story for those that haven't any prior knowledge about it, but at the same time, contains all kinds of little in-jokes and references to the books, mini-series and radio series which I just dig so much. For example, the music played during the very first Guide scene is the theme from the radio series. Whenever Ford swears in the film, he utters the word "Belgium". Zaphod's psychologist showing up on a background display with his line, "Zaphod's just zis guy, you know?" The mention of the Restaurant at the End of the Universe.
Sure, they changed a bunch of things for the film. Some of the changes are good. I found Sam Rockwell's "lunatic cowboy" portrayal of Zaphod to be a nice change from the "self-absorbed beatnik" that always shows up in British dramatizations. The Arthur/Trillian plot was played up, but not enough to detract from the film, and the Vogons got more screen time, since it's a movie--you
need a villain. (Same reason why Saruman got a bigger part of the Lord of the Rings films.) At the same time, some changes I thought were a little half-baked. While I think it was a nice addition to the story, allowing the core plot of the first book to fill the movie, the whole John Malkovich/Zaphod's head thing didn't really go anywhere. Also, while the Vogons are interesting, they aren't quite enough to be the main villain--I think the Krikkits would have been much better, but they also require far more setup to make threatening, which would have further detracted from the plot.
All things considered, as an adaptation of a series with a fanbase bordering on Sci-Fi Fanatics, the film of the Hitchhiker's Guide is very well done. It doesn't cover everything in the Guide, but it covers enough and it does so well.