Would you like to be able to see your own body when you're in 1st person ? I know few modern games did it and few have done it right but if given the time to look good, it would be a nice immersion.
Also, I'd like to be able to move the head independant from the body the way it's done in ARMA (you hold ctrl or 1-click toggle it and move the mouse and you move around only the head). Yeah, I know, "what about consoles?". Meh, this won't be in the game anyway, so what do I care
This feature allows for the use of an incredible tool : TrackIR. For those who don't know what it is, it's a infrared detector that tracks the movement of your head and moves the head of the character accordingly. It is a nice immersive gadget ! Here's some video :
How it works : http://www.youtube.com/watch?v=_AO0F5sLdVM
What it looks like in-game : http://www.youtube.com/watch?v=ZluGLQ6X4MQ