The H2G2 game was alright, but Starship Titanic was really enjoyable, in that uniquely 90's point-and-click computer game sort of way.

Not sure I'd want a "modern" H2G2 game though; keeping it 2D or prerendered screens like Starship Titanic leaves some of the environment to the players' imagination/interpretation and that's really important to me in things based on books. When the world is fully rendered and you can walk around in it freely, it clashes too much with my imagined version of people, places and things.