There are two Dirk Gently books, Dirk Gently’s Holistic Detective Agency, and The Long Dark Teatime Of The Soul. They are both humorous, intelligent, complex, and highly imaginative. And very original, I’ve not seen anything quite like them.
Douglas Adams of course wrote The Hitchhiker’s Guide To The Galaxy. The Dirk Gently books are also humor, but not at all as far out as HHGG. They are more ‘realistic’ as far as that can be said of books which involve time travel, ghosts, and gods.
I really appreciate them, it’s extremely rare to see such a combination of intelligence and imagination and humor. I think only Terry Pratchett is in the same league.
Adams was working on a third one when he died at 49 around the millennium. It was published with other diverse scraps, but was clearly only rough ideas.