Back in the 80s there was Zork (see "Attention Adventurers!" for versions you can download and play offline), an amazing text-based adventure from InfoCom. of course, with the graphics revolution that made 3D worlds and FPS games the norm, these games didn't hold the attention of the masses.
They games are pretty cool, though .. and anyone who loves to read will enjoy them; they're quite like an interactive book.
Digg posts "20th anniversary ed of the hitchhiker's guide text adventure", pointing to "THE HITCHHIKER ADVENTURE GAME by Douglas Adams - 20th Anniversary Edition"on the BBC site.