The cast is fine, the movie has a certain polish to it, but in the end, you cannot invest time in these characters because there is no reason to.
The story follows the struggles of poor Arthur Dent as he discovers that his best friend is not from Earth. The bewildered Dent learns this moments before Earth is demolished... and this double whammy discovery of alien friend and Earth's demise should guarantee at least a hearty belly laugh... it doesn't. Then, to add insult to injury Arthur must Hitchhike his way across the Universe to safety. A flat script, actually penned by Adams is the result of a watered down concept hijacked from a very funny and lively concept.
Much detail is left out (expected), but much of the reason for joining the adventure is as well (unexpected). Perhaps Adams' script was penned for a culture that craves sterile, single serving solutions to all of lives mundaities... or perhaps it was completely re-tooled after his untimely death from a heart attack last year. Who knows, who cares?
Pass on this film... Instead, pick up the book, hear the radio show, or try to obtain a copy of The BBC miniseries of the same name, done in the early 80's... much cheesier fare, much better results.