Seems kind of nauseating- I guess that's the price you pay for looking cool.
Moose, are you suggesting a "camera locking" option that keeps the camera facing in a certain direction while still allowing the player to change where their weapon is swung with the mouse cursor? For the purposes of allowing for cool combat moves, I feel like that might work while mitigating motion-sickness, and it doesn't seem that hard to implement (but what do I know, I've never worked with Unity camera controls).
Maybe you could hold a button close to WASD (C or V or something within reach of the left hand) to lock the camera and letting go of it snaps the camera back where it should be facing. I have no idea if that would end up being too janky/buggy to implement, or even if it's what Moose had in mind when he posted this.
Fish, do you have any opinion on Moose's discovery or my suggestion?