Sherlock Holmes observed that once you have eliminated the impossible, then whatever remains, however improbable, must be the answer. I, however, do not like to eliminate the impossible.
We don't actually get to meet the titular detective until some way into the first book, and until the sequel, Dirk isn't a viewpoint character. This role is filled in the most part by his old college friend Richard MacDuff, although admittedly Richard shares this position with an alien robot monk, a ghost, and the electric monk's horse (the one that materialised in the bathroom.) Just as in Hitchhiker's Guide to the Galaxy, much of the sciencey-technobabble goes straight over my head, leaving me somewhat discombobulated. Unlike Hitchhiker's, however, much of it comes back later, by which time it actually makes a little bit of sense. I found myself reminded a little of Doctor Who, which, I later discovered, was with good reason: the time-travelling Cambridge don was recycled from a disused Doctor Who script - written by Adams himself.
Although the adaptations use elements of the books, they are generally only minor plot details with original stories built around them. Rather than being out-and-out science fiction, the BBC stories flip-flop over the genre line from surreal realism into fantasy, notably the episode dealing in robotic engineering. I'm not really qualified to comment on the advances in artificial intelligence, but I haven't yet heard of anything resembling the plot twist in episode 2 in real life!