I have to say that I didn't much care for the books and thought the pilot episode was actually better than the book. I thought Addams writing was going downhill during the later HHGTTG books and, although there were some inspired moments in the two Dirk Gently books, they were a shadow of his best stuff.
But the pilot episode was clever, funny and very well cast. It's a great basis for more of the same and new adventures by different writers. I hope the series (or whatever it turns out to be) will be as good or better than the pilot.