I am always interested in this subject and that's because it really manifests in different ways in every person.

For example, people had various theory, like good graphics make motion sickness because they are so realistic you believe you are in the game. That's not true as I was getting very easily motion sick with wolfenstein3d (yes, the original 1991 id title) but I wasn't affected from Doom or very recent FPS. Others said it's the very low framerate. Again not true in a universal sense, since I was fine with Doom's locked 35fps but when I first try to play Quake in a fast computer in smooth framerate (60fps or 70, can't remember), everything was moving so fast that I wanted to throw up. Of course that may be also how the player moves, slow/fast, camera bumping up and down (it never make me sick in Doom though) and maybe sometimes also very close rooms with narrow walls could.

Another one that really make me feel awful was Halflife. And interestingly, both 1 and 2. I still wanted to finish them though, I was playing like half an hour for each before I had to quit. The effect was so strong I had to look away from any game for the rest of the day. Not sure why, my best bet is the way the player moves/slides in both of these games. I am not really sure why I had problems with these games (maybe I still have) much more than any other franchise.

So, for me it was wolfenstein3d and halflife 1,2. Like 10 or 30 minutes and I feel awful. I was better with Doom and Duke3D (not perfect if I play for many hours, but better with Doom and a bit less better with Duke3D and Build engine in general). I got used to Quake though. And I have been playing many modern FPS and it's fine unless I decide to play for more than 4-5 hours in a go. I did had my share of motion sickness from Oblivion or Borderlands, but after long plays where it makes sense to stop.

Of course there is this talk about higher FOV helping against mosickness and I might want to try this again with HL1 and 2 if they allow this to change.