My introduction to The Hitchhiker's Guide to the Galaxy was through the movie - which I found to be totally not-funny, and a waste of time. So I was put off by bothering with books as well. But recently when I was at a library, I decided to try it, because it is supposed to be one of the SF Masterworks books, which is a pretty decent list. And to my surprise, I really enjoyed it. It was funny, unusual, but more importantly it was an achievement as a writer (I'll come back to that in a minute.)
So I got the second and third book too. And as I am not that great at reviews without spoilers, I will share one paragraph, and if you find it funny, you will enjoy the book. This is from the second book, The Restaurant at the End of the Universe.
It is known that there are an infinite number of worlds, simply because there is an infinite amount of space for them to be in. However, not everyone one of them is inhabited. Therefore, there must be a finite number of inhabited worlds. Any finite number divide d by infinity is as near to nothing as makes no odds, so the average population of all the planets in the Universe can be said to be zero. From this it follows that the population of the whole Universe is also zero, and that any people you may meet from time to time are merely the products of a deranged imagination.
To come back to it from a writer's point-of-view. This series is completely unorthodox. It is crazy, full of exposition, and let's not even talk about POV shifts. My point is that all the rules of writing that you have ever been told, are all broken. Except one. It's a great story.
Terry Jones said in the introduction of the book, "He's (Adams) the only novelist I know who can make ideas a page-turner."
And that's the key. This is not a plot driven or even character driven book. I wouldn't know how to define it. It simply is what it is. But it works, because of Douglas Adams' mastery of the writing craft. There may be exposition, but there are no wasted words. Every sentence serves the purpose of the story. Rules are broken but the story works, because it is handled by a writer who knows what he is doing.