In science fiction, the writer sets up an experiment in which humans are the variable. "The Hitchhiker's Guide to the Galaxy" is exemplary: it begins with a bunch of humans in a human environment, then takes a random human and throws it into a series of extraterrestrial environments that always present new conditions.
The film version of "The Hitchhiker's Guide to the Galaxy" works well because scene corresponds neatly to a different experiment. These experiments are never resolved, but this tension flows through the series of scenes. This is a technique proper to epic theater. I should also say that the film works because Mos Def is a great Ford Prefect, no matter what the fools on the IMDB discussion boards might say.
After watching the film I went back to look at the book, thinking that I'd be rediscovering the Borges of sci-fi. Unfortunately this wasn't the case. I was a little crushed to find that the film uses a more fitting vocabulary to relate the story than Douglas Adams himself. There went my career as a lecturer on the connection between Borges and Hitchhiker's Guide. (It exists when you're talking about the movie!!)