It is, to paraphrase Douglas Adams, almost, but not quite, entirely unlike a Hitch-hiker novel. In Mr Colfer's defence, he doesn't go out of his way to copy DNA's style, which would quite possibly have made a bad book worse. I also laughed once.
But my main problem with this book is that it just misses the point by a country light year. I can't even remember what Arthur Dent did in this book. I'm pretty sure he was there, but far from being the continuing misadventure of an everyday bloke from Earth, And Another Thing seemed to be more interested in the (now single-headed) Zaphod having a little jolly around the afterlife.
I got the impression (as I did with the film) that this was a bunch of DNA's previously discarded ideas retrieved from under his desk and thrown together by someone who probably didn't know exactly where his towel was at the time. There's even a recycling of some of DNA's good ideas, like naming a character Hillman Hunter.
Nope, for me, the Hitch-hiker story ended with the Quintessential Phase. And Another Thing... is, to paraphrase Ford Prefect, mostly pointless.