Some time ago, I was thinking of a problem that Aubrey touches on in one of his recent comments: how can you make emotional input emotional?
It's not that difficult to create an intellectual system for inputting emotions. Say, the mood-o-meter: select 'happy' from a menu to indicate you're happy. It's been tried a couple of times in the history of mankind. (So when I say it's not difficult, I mean one can sort of see where to go, even though nobody has done a good job of it yet and you'd probably have a really hard time convincing any company to invest money in it. But anyway, that's a different entry.)
So how can you make emotional input emotional? How can you make a half-way decent attempt at capturing the honest emotion of the player? I came up with something that's obviously flawed, but that I nevertheless find fascinating. Imagine a dialog screen where you see two people facing each other from the side. Imagine you're controlling the person on the right. You're using some controls, the arrow keys or something, to select phrases from a list. Normal conversation interface stuff. At the same time, you're using the X axis of the mouse or an analogue stick to control your conversation 'stance'. Basically, we're looking at conversations as power struggles. You can either lean forwards to become more pushy and domineering, or backwards to give in to the other, or try to stay centered. (The other person's movements might affect your stance, so there could be a balancing element. You could also add some simple resource management, to simulate poise or energy. I never developed the idea very far.) You would of course see the stances of both characters: they would lean forward and backward, changing their posture, etc.
The core idea is that an analogue, short feedback loop input mechanism should allow for very intuitive emotional input. A secondary, but crucial idea is that a horizontal physical movement is mapped to something that also intuitively feels horizontal.
Obvious flaws are that there's nothing really logical to map to the Y axis, and a dialog system entirely based around domination, while promising, is also gimmicky and not generally usable.
Dialog systems, now there's a topic for a million blog entries...
I think Phil Harrison once mentioned that the PS3 should be capable of more advanced image analysis than the PS2, and that it might be possible to detect emotions, so maybe we'll find another solution in a few years.