Swaying camera views, bulked bubble visions, know what I'm talking about?
Example - Morrowind. Took me weeks to get used to the game before I could play it without getting virtual motion sickness. I played it for two hours one time, having too much fun, after that I really felt like throwing up. Back when Morrowind was first released, it really was one of those must-see games even if you don't like that genre.
Gothic 2 was bad as well. Lots of people loved that game. I think it's great judging from the reviews, but the perspective from which the game is played just made me horribly sick. I couldn't stand it. Everytime I turn my character around, I felt like I was going to spin off my chair.
Medal of Honor, The Suffering and as far as I remember, any game played from first person viewage had that same effect on me. Although some are worst than others. I got used to Morrowind, but not Gothic 2. Medal of Honor was pretty ok after a few days of playing, but Soldier of Fortune II was really bad and I never could play that one for more than half an hour. I can take playing the Suffering for about a little over an hour but not more. So there seems to be degrees of tolerance for me.
However, there never was a problem with driving games, which is usually played with a view from within the car, or behind it. So far, I haven't felt sick even after playing Burnout 3 or Gran Turismo 4 Prologue for more than two hours.
...Which leads me to suspect it is not the first person perspective that is the problem, it is the swaying camera. It's like watching Blair Witch Project, the camera sways because it is on the shoulder of the person who is holding it. You sway when you walk, in order to keep balance but your brain counters the consciousness of it because it knows what you are doing. So when you walk, or turn your head, you don't get yourself sick. However someone watching a movie made from your perspective entirely may end up feeling very sick after watching it for a while.
Game devs making these FPS or FP-RPGs might want to think about stablising that camera view instead of having it sway the way it does everytime the character turns, and calling it realism. It's not a big problem. It's true that if you game on these long enough you get used to it, just like people get used to being on boats and not getting sea-sick after a few days. But I do know of people who avoid these games because it makes them feel sick, and they don't exactly have the time to get used to it. If the game is being touted to be good, I try to play them. But if I can't get used to the game after some time, I'm not likely to be able to finish the game as I won't enjoy it.