The orange box does it to me also. Cant play for more the 20 mins without feeling ill. Same happen to me with tribes 2, about 10 mins into gameplay.
I'm good with everything else. its just the magic combination(rendering engine + FOV) for some folks.
Just recently COD4 on 360 single player has been giving me fits, but multiplayer i can play all night no issues. Thinks its the difference in game style, less cinematic jarring and i'm looking all over the screen in mulitplyer instead of having the story told to me in SP.
where as with oragne box it has to be the engine and FOV as both TF2 and HL2 start making me ill.