The Hitchhikers Guide has this to say about movies:
A movie or a motion picture is a series of still pictures flashed onto a screen in rapid sucession designed to fool to observer into seeing motion via the phenomenon of persistance of vision.
This effect for the species known as human beings occurs at the unlikely rate of 16 frames a second, though this figure can be lowered under certain conditions like the consumption of alcohol but this may lead to still objects appear to be moving as well.
Please note that this effect of persistance of vision is species specific. Whereas 16 frames a second works for humans, 22 is the figure for the domesticated cat and 4,866,924,339,777,202,548,963,102,536,787 is the figure for the sludge monsters of Splattican VII - also note that their entire life span is only about a second and entire religions have sprung up whilst a single picture was flashed on a screen.
In general it is difficult to make a movie which is better than the book it attempts to portray, this is mainly due to the fact that text contains so much more vivid imagery and is generally examined for longer periods. Such can be said for the movie of the novel of The Hitchhikers Guide but given the surreal nature of the book, an accurate depiction may be nigh on impossible.
There is one notable exception to this however and this is The Lord Of The Rings trilogy. This one example where the film is better than the book is because the book sucked worse than a class five black hole whereas the film only sucked as bad as a class two black hole - it still labours the point that both sucked immensely.