The Restaurant at the End of the Universe (1980) picks up where the Guide left off, furthering the adapted radio adventures of Arthur Dent, Ford Prefect, Zaphod Beeblebrox, and Trillian. The book inherits all the strengths and weakness of the first adaptation, while attempting to remediate the radio series's flaws.
The strength of this book remains Douglas's wit and humor, his stunningly realized comedic characters, the bizarre scenes, and his ability to highlight the flaws in our own technological society. The weaknesses of this book remain the story. That is to say, it doesn't have one. Well, it does have one, but it doesn't really matter.
Douglas does try to create an overarching story to hold the work together, with Zaphod's search for the man who rules the universe, but we never really care. He even rearranges the end of the first radio series and the entirety of the second radio series to make it all happen, but to no avail. Even for a Hitchhiker's fan like myself, the book looses its wind in the middle, begging you to put it down.
Overall, a work of comedy must work as comedy before anything else, and in that, this book succeeds. The book works where it matters most. But if you want a good overarching story that your local writer's group won't tear apart, you'd better read something else.