
In Dirk Gently's Holistic Detective Agency, Dirk is drawn into a four-billion-year-old mystery that must be solved if the human race is to avoid immediate extinction. In The Long Dark Tea-Time of the Soul, the discovery of a headless body found in a sealed room plunges Dirk into a mystery where the interconnectedness of all things is tested to the limit.
https://en.wikipedia.org/wiki/Dirk_Gently%27s_Holistic_Detec...
https://en.wikipedia.org/wiki/The_Long_Dark_Tea-Time_of_the_...
In the novels, a stuck sofa is revealed to have got there because a retired Time Lord, Professor Urban Chronotis, briefly materialised his TARDIS in such a place it provided a doorway. So the books are extremely loosely tied into the Dr Who universe.
Don't let this put you off.
The Lord of the Rings is spectacular. The movies were remarkable feats, but they missed the trilogy's heart (and ruined some great characters). It's dense reading, but the prequel The Silmarillion is perhaps the only successful epic mythology written in modern times.
C. S. Lewis' "Till We Have Faces" is a remarkable adaptation of the Cupid and Psyche myth, from the perspective of Psyche's sister.
I loved Spider Robinson's Variable Star, based on an unfinished outline by Robert Heinlein.
So I say it was a good thing overall. Even though it was also sad because it was the unfinished writings of a dead author I love.
Further reading for anybody who enjoys Adams, Wodehouse was said to be one of his influences: https://en.wikipedia.org/wiki/P._G._Wodehouse