I thoroughly enjoyed the first book, but I liked each subsequent book less. Since it's been quite a while since I read them I couldn't tell you why.
Few movies can make enough money at the box office if only the fans of the books show up, so they also have to grab the people that aren't huge followers of the written version.
I suppose I fall somewhere in the middle and when I went to the movie today I took my two sons (11 and 7) who haven't read the books at all and were only familiar with Hitchhikers from the movie trailers.
The few reviews I read seemed to say the movie was only for the fans. I disagree with that. The three of us enjoyed the movie and we certainly don't qualify for the Hitchikers cult. I enjoyed the visuals, the cast for the most part was well chosen and I think they did justice to the humor of Douglas Adams.
I can't imagine anyone is going to have a problem following the general storyline which has to do with the destruction of the earth to make way for an intergalactic expressway and I think most will appreciate the end which ties things up pretty well.
Of all the end of the world movies out there, Hitchikers Guide to the Galaxy is certainly the most original.
Go see it.
Get the big popcorn for me, but hold the butter.
Keep the Adventure Alive,