I thought it was entertaining, and I liked it but I don't think it rocked. Zaphod was absolutely hilarious though. Also, as far as most of the humor being in the writing goes, the movie had a small amount of narration, such as when the guide to the galaxy was quoted in the books.
Keep in mind that the screen play was written by Douglas Adams, which is both good and bad because it lowers the chances of a sequel with him being dead and all.
I thought it also focused too much on the relationship between Arthur and Trillian. It seemed kind of like a love story. That may just be me though.
Anyway, GO SEE IT!!