I just installed S.T.A.L.K.E.R. - Clear Sky inspired by our earlier discussion. I haven't played it much yet because there was a headbobbing motion in it that made me feel quite sick even after just a minute or so. Fortunately, I checked on the net and I wasn't the only one who got motion sickness from this game. I just installed a little hack someone made that should take care of the problem, hopefully it will.
You'd think that if your game makes people motion sick because of an easily fixable headbobbing, the developers would do something about it.