I've seen the TV series and am currently listening to the original audio series which I've got on my PC. If you haven't heard, read, or seen it then you have missed something special and very very funny, and you should correct this error as soon as humanly possible.
This film is based on the novel by Douglas Adams, and stars Martin Freeman from The Office as Arthur Dent, along with the always excellent Sam Rockwell as Zaphod Beeblebrox, and Mos Def as Ford Prefect. Other notable names are Bill Nighy as Slartibartfast, John Malkovich as Humma Kavula, Alan Rickman providing the voice of Marvin the Paranoid Android, and Stephen Fry as 'The Book'.
I'm really glad that the lead has gone to an Englishman, and I think Sam Rockwell can get away with playing the character Zaphod. Stephen Fry as 'The Book, a brilliant choice, Alan Rickman as Marvin...yes, he always plays someone with that dour monotonal voice, excellent choice of casting so far. Stick Bill Nighy in there, yes so far so good. And then....who shall we get to play Ford Prefect...this is a joint UK/USA venture....I know....The hip-hop star Mos Def! What? I know that he started as an actor and then went into music but I don't know if he can pull it off. I know Hollywood is a cynical place and films are actually only made for money and not for any artistic premise (see the Star Wars rip-off preludes) but I suppose the money it brings has been able to bring together a good cast of actors (minus rapper Mos Def) and I hope the film does well and hopefully brings people back to the original Douglas Adams, the original novel, the TV series, and other Douglas Adms books such as Dirk Gently's Holistic Detective Agency.