IF as a genre, fundamentally unchanged for more than twenty years, evolved in a world of gaming where graphics were non-existent and words were the sole medium of expression. The game described locations, objects, and actions in text, and the player controlled the story’s protagonist by typing commands in English (or any other natural language in which the story was written). As a player, you had to rely on your imagination to fill in the gaps.
In the time since, technology has allowed designers to create games that realize their visual ideals. And many of these games have captivating stories and excellent puzzles, just like good IF games. —Frank Pape —Interactive Fiction: Words vs. Pictures (FrankPape.com)
A good introduction to interactive fiction.