For the past while, I've been slowly working on designing a game based entirely upon a conversation, and have been thinking a lot about
puzzleless adventure games as a result. Certainly, puzzlelessness is a lot more prominent in IF than in graphical adventures (or so I've heard; my experience with IF is admittedly rather limited). Still, with more and more underground graphical adventures getting made, I'd quite like to see more experimentation in this regard.
So my question to you wonderful folks is as follows: what would you say would make a puzzleless adventure game fun to play? The ability for multiple outcomes and for your actions to make a difference in how the story progresses, so it won't just feel like you're clicking through a machinima movie? High interaction density with your surroundings? Just plain good writing, art direction, etc. (which, of course, is important no matter what)? Does it need to be a lengthy epic to be worth playing? And of course, is it still a game if it has no puzzles?