Got to know of this book from a junior in my B-School. And am thankful that I did. The entire series of HGTTG (6 books altogether including the first one, Mostly Harmless, So long and thanks for the fish, the restaurant at the end of the universe, etc.) is one good book and is among my favorites along with Yes Minister, Yes Prime minister, Malgudi Days.
Douglas Adams has taken us on one hell of a space journey, when in the first five minutes Earth gets destroyed by aliens making way for an expressway. From there, the two travellers in the book go thru amazing things like the worst poetry in the universe, a planet that was supposed to be the factory for creating planets, a restaurant at the end of time where there is a special show showing the end of the universe, a robot with the brain the size of a planet, the discovery that Earth is nothing but an organic computer and lastly, the discovery that man is only the third most intelligent life on Earth.
It is science fiction, comedy and imagination at its best. I would recommend this book to anyone who loves reading and specially those who love sci-fi.
It also has philosophy in that the search is on for the ultimate to Life, Universe and everything. The problem comes up when the adventurers manage to find the ultimate answer but do not know what question it answers. And hence the search is now on for the ultimate question.
My suggestion: Read this book sometime in your life, even if you die laughing while reading it.