...it's a good movie! I managed to see this movie the other day, I thought it was great. The casting was superb with the best being the voice of Alan Rickman as Marvin and Sam Rockwell as Zaphod Beeblebrox. I did have to do a double take at first cause I thought Sam was Chad Kroeger of Nickelback...
I haven't read the book in probably 10 years and had forgotten some parts, so I don't think you need to read the books to understand the movie, although there are some hidden things that only the die hard fans would recognize.
One of my favorite parts of the movie involved the improbability drive of the space ship Heart of Gold where Arthur Dent... nah, I won't spoil it for you you'll have to see it .