Game idea:

An interactive fiction MMO. No character creation, leveling, or fighting, just lots of text.

Dr.: Welcome to the experimental labs of Aizen corp. I am doctor Lee, and I'll be your guide in this new world. I hope you'll be cooperative for these experiments. There's a mirror on the wall over there, though you probably won't recognize what you see.

Essentially, it'd be a story in which the players get to interact with the doctors and assistants running the "inter-dimensional experiment". The primary challenge is likely to come in the form of making the interactions feel realistic. The players should be allowed to give unusual answers to questions as well as to ask questions themselves, so making the AI able to handle that would be awkward. A lot of writing will need to be done to create responses to all the various things the players have to say. (and the writers will have to continue producing such writings as the game is played).

A large part of the idea is to tear down the 4th wall, and let the players talk about things they see/experience that the NPCs don't. Though ideally the players would be encouraged to say/do whatever they want, whether it be lying, or telling the truth (either of which could confuse the NPCs). I want the player to be a part of the game, not just the character they control.

Another part of my interest is to see how people respond to always being in a randomly chosen body, and having to deal with the NPC's assumptions.