Good Omens
Why it's similar
Good Omens is what happens when you put two of the funniest writers in speculative fiction in a room together. Neil Gaiman and Terry Pratchett co-wrote this novel about an angel and a demon who have grown comfortable on Earth and would rather not see it destroyed by the Apocalypse, thank you very much. Like Hitchhiker's Guide, it takes a cosmic premise and fills it with deeply human absurdity. The Antichrist gets swapped at birth and ends up in a quiet English village. Everything spirals from there. The humor operates on the same frequency as Adams.
Both books find comedy in the collision between the mundane and the cosmic. Adams had Arthur Dent worrying about tea while the galaxy crumbled. Pratchett and Gaiman have an angel worrying about his book collection while Armageddon approaches. The wit is literate, the satire is sharp, and the affection for humanity is real underneath all the jokes. If you want one book that scratches the Hitchhiker's itch, start here.