From IFWiki

Puzzleless games break from the traditional pattern of using puzzles in order to control the player's movement through the game world and story.

Some such games provide the player with a more fine-grained level of interaction, focusing tightly on a particular situation and allowing the player to affect unfolding events in more subtle ways. In particular, some games concentrate on conversation between the player and NPCs, in which the player's goal is simply to converse, as in Emily Short's Galatea.

Other puzzleless games lower the level of interactivity altogether, shifting the balance of power toward the designer, making the experience more like a traditional narrative (in which the reader need not perform any non-obvious interactions in order to experience the whole story) and curtailing the player's ability to engage in incidental or tangential interaction.

See also