Oh man - you MUST read the books! The movie is OK - but the books are absolutely fantastic. If you aren't a reader, then load the audiobooks on your DAP. Douglas Adams was a brilliant writer. He was full of great one-liners, for example: "I love deadlines. I love the whooshing noise they make as they go by." Or, this one: "If you try and take a cat apart to see how it works, the first thing you have on your hands is a non-working cat."
He had zillions of those: http://www.goodreads.com/author/quotes/4.Douglas_Adams
Seconded. That line about the deadlines is one of my all time favorites. I also like "The ships hung in the sky in much the same way that bricks don't." I would say that the writing, far more than the plot, was the real draw for me. The introduction said that reading Douglas Adams will permanently rewire your brain, and I have to say it's true. I found myself finding the humor in everyday situations and commenting darkly on it far more often after I read the series. I also instinctively look for bizarre connections between things now, the way Adams clearly did. You know, the word "genius" is thrown around far too often these days, such that it's become cliche. Douglas Adams is one of the few people I actually think is deserving of the word.
In fact, because of all this I've just become inspired to read the series again. I'll have to fetch my copy off the shelf.
I like Adam's other series, Holistic Detective, Dirk Gently. Long Dark is a really great read.