Mostly Harmless (2000) by Douglas Adams shows demonstrates what happens when a novelist acts passive-aggressively towards his publisher. While technically a Hitchhiker's book, the novel lacks much of the charmingness that a Hitchhiker's book usually contains. If you thought that our heroes were sent through the ringer in previous books, they're positively steamrolled flat in this one. If there was any book that the fans wouldn't want, this is it.
This book sends a message to the publisher: if you want an even less sympathetic Hitchhiker's book, I dare you, just dare you, to make me write it.
On the writing side, the whole thing works as a story, the descriptions continue to engage, and the plot still rolls along nicely. However, without its metaphorical heart of gold, it's got a metaphorical heart of lead. I figure that Douglas must have played a rousing game of Fallout before penning this book, just to reacquaint himself to bleak.
If Le Miserables were written as a comedy, it would read like this. As a film, it would be directed by Lars von Trier. If it was a play, it would go on after Hamlet just so that the audience could get properly warmed up.
If you aren't up for it, then skip it. Your happy universe will be better off. On the other hand, if you love the humor in Fallout, then this is the book for you.