"And Another Thing", published in 2009, is the sixth book in the Hitchhiker's Guide to the Galaxy trilogy. Since the author and creator of the series, Douglas Adams, had passed away, the book was written (with the full approval of Adams' estate) by Eoin Colfer, a writer best known for the Artemis Fowl series of Young Adult novels.
For those familiar with the Hitchhiker's Guide series, the book is much of what we have seen before. In fact, the book opens with the earth being threatened by destruction by a Vogon fleet, which Arthur Dent and Ford Prefect must escape, in a series of wacky and (forgive the importation from another hallmark of British science-fiction) timey-wimey adventures. Through a series of improbable events and characters, the book reaches some type of happy ending, and the galaxy survives for a bit longer. The full plot would be hard to explain to a non-reader of the series, and trivial to explain to a reader of the series.
Eoin Colfer is very respectful to the source material, and his authorial voice is already close to that of Adams'. Without a byline, it would be hard to guess that the book wasn't written by Adams, although I would say that Colfer's tone is in general a bit less weighty and more slapstick than Adams' was. And the book was entertaining, and for any self-respecting geek, reading a Douglas Adams book is pretty much mandatory, even if Douglas Adams didn't write it.
The biggest problem with the book is probably that it is thirty years since the original work came out, and the wackiness is a little bit less wacky. After all, many more modern readers are familiar with the series deconstruction and parody of galactic empire tropes than are familiar with the straight take of galactic civilization found in works like The Foundation series. So while "And Another Thing..." is a fun read, its main purpose and interest has been, by this point, mostly exhausted.