Simply put, I liked it. Yes, it was different from the books that Douglas Adams wrote. To expect anything else would be utterly ludicrous. I've seen quite a few people complaining about this - "Adams would have done it better" and so on. This is, of course, true. However, it is also unimportant - like saying that liver would taste better if it was steak.
I went into this book with the mindset with which I approach a movie based on a book - I was determined to try to enjoy the book for what it is, rather than nitpick all of the inevitable ways that it isn't like what came before. This tactic was, as usual, quite successful. Eoin Colfer cannot write the same way that Douglas Adams did. He also did not try. What he did do was to write a new novel set in the Hitchhiker's Guide "universe," but in his own style. Of course, there were numerous homages to the original novels, but these appear to have been done in tribute to the late Douglas Adams, rather than in mimicry of him.
Story-wise, Colfer managed to very cleverly extricate our heroes from the rather unenviable situation in which they found themselves at the end of Mostly Harmless. I won't go into any great detail, but suffice it to say that a certain stolen spaceship was involved.
From this point, the author re-introduces a few minor characters from previous books (they become major characters this time around), the Vogons doggedly pursue the annihilation of the earth and all who dwelt upon her, a group of expatriate humans begin interviewing candidates for the position if God, and Zaphod reveals a new use for his second head.
Altogether, I thoroughly enjoyed this book. I started chuckling on page one, and remained entertained through to the very end.
If you want this book to be another Douglas Adams novel, just walk away now. You're never going to be happy with this book, and it's better if you just don't read it. If, however, you're willing to take this book as something "one step away" from the Hitchhiker's Guide books, then dive right in. Just bring your own Pan Galactic Gargle Blaster.
This review will also be posted on Goodreads.