[adamesque]

We did one demo that was more or less floating above static terrain, and another with Half-Life 2.

My own nausea didn't actually start up until HL2. We were playing on a laptop (probably not enough horsepower), using slightly unfamiliar keyboard & mouse controls. So some movements were very fluid & second-nature to me, while others were jerky and off because of the slightly-off control scheme.

It's possible the most nauseating moment was taking the headset off, actually. Up to that point, my mouse hand had been a pretty accurate proxy for my in-game hand and arm, but taking my hand off the mouse and then ripping the "world" away with that same (now "phantom") hand was deeply disconcerting.

But it's also possible the nausea built up slowly over the course of playing. I'd love to spend more time with it to see if it's something you really can adjust to.