This movie differs from the book on a few things, and some of them were points that I thought critical. There was also a compression factor involved -- rather than the way some things came about in the book over time they had to just have come about in the movie. I'll watch this movie again after it comes out on DVD and perhaps up the rating on it at that time.
And yes, I was expecting it to be different from the book (for example, John Malkovich plays a character that didn't exist in the book at all), but there are one or two differences that I don't think should have been differences (Spoiler: For example, Trillian likes Arthur; Zaphod isn't green, and his heads are vertically oriented rather than horizontally oriented). My thoughts are that maybe knowing about these differences when I watch it next (on DVD probably) I can feel justified classifying it as recommended (2), but just not right now.