For the most part they kept to the cast of the earlier radio play although both Ford Prefect (David Dixon for Geoffrey McGivern) and Trillion (Sandra Dickinson for Susan Sheridan) were recast.
It tells, as I'm sure you know, the story of Arthur Dent (Simon Jones) who, on the day the local council decide to demolish his house in order to build a bypass, discovers that not only is his friend Ford an alien from a small planet somewhere in the vicinity of
To help him better understand where he's ended up Ford gives Arthur a copy of The Hitchhiker's Guide to the Galaxy an electronic and somewhat eccentric electronic book (voiced by Peter Jones) that via little animated entries provide him with snippets of information about the galaxy.
I was a bit too young to catch the radio play so this series was my first exposure to Hitchhiker's and is still my favourite. From the cast and the acting, through the animation and Paddy Kingsland's incidental music to the wonderful and inventive script, I love it all.