Pigeons in the Park is a conversation piece (game is probably the wrong word) by Deirdra Kiai, somewhat in the mold of interactive fiction conversation works, but designed in the Wintermute engine and accompanied by graphics and sound. (I gather. I played it with the sound muted because I needed to avoid disturbing people around me, but others have mentioned that there’s a soundtrack.)
Pigeons in the Park is at the extreme hypertext-like end of the interactive conversation genre. There’s no text parser, just a short menu of options to speak, and since the amount of content is relatively small, you can run through most of the interesting options in the dialogue tree in ten minutes or so of play. It also reminds me of some of my own earlier work in that it’s quite self-referential: most of the actual content of the conversation is about story-telling in games. The protagonist is also a bit of a blank slate.
Embedded in the conversation is a question: how do we make these exchanges emotionally affecting? How do we write interactive conversation that is moving as well as amusing or arty?
I still think the answer has to do with not starting from scratch, but beginning with characters who already have some history. But I’m really intrigued to see this kind of problem being addressed in other media than textual IF.
Emily Short's Interactive Storytelling 
Characters that have some history and interact with each other in an emotional context as well as personality traits that are large broad strokes. Most people find characters touching and more real the more singled out they are in design.
What I mean by this is having a powerful character trait that stands out. A character who is full of anger, and is too proud to back down. A character who is depressed all the time, and is the victim. Another character who is completely insane and acts unpredictably. Or a character obsessed with their own machismo.
People tend to feel a connection to these characters and get a more profound emotional reaction. this also allows players to get attached to NPC’s quickly- it’s very easy to show this character’s personality in a few actions played out in a scene or two. This adds a dimensional quality as well, esp if the characters change through the passage of the game, become different.
Anyway, I’m just a beginning IF writer, this is all stuff I pulled from my own short stories and the novel in progress.
I would have thought that a better way to ignore (if not avoid) those disturbing people around you would be to play with the sound *on*.
What does successful conversation in IF have in common?
I think there is a Kantian answer to this question. When used successfully, the conversation becomes an end-in-itself, not a mere means to another end (perhaps the acquisition of information, or the manipulation of another person).
In Pigeons in the Park, and in Galatea, the player’s intent is to be in the conversation, and to explore the conversational landscape he has found himself in, not to try and escape (to use the conversation to further some other external goal).
There have been some not-so-successful pieces of conversation IF, though; and a handful in which conversation worked well despite a larger setting. (“Elysium Enigma” seems at least worth considering in that category — the player has tasks beyond the conversation, but interaction with the primary NPC is a vital part of the story, and is fairly developed.)