I stopped playing games about 10 years ago, but thought I would come out of the break to play Portal... I did, and was very saddened to find that I just couldn't play it because it gave me really bad motion sickness and headaches. The nauseating feelings kick in after just 60 seconds of gameplay (and no, not just when going in and out of portals -- even when I'm simply walking around without making portals the headaches come in).
I hope more research is done on this, and some solutions are found, because I really want to finish playing Portal. :)
I've been playing FPS shooters for most of my life. But I've had to stop.
For some reason HL2 would give me headaches. Really, really bad headaches. I thought it might be the Engine, or me being tired. But I don't get headaches playing TF2 or Dystopia, both of which use the same engine. Surprisingly, Portal and Portal 2 didn't give me as bad headaches.
Later games are hit-and-miss. Bioshock I didn't suffer. Bioshock Infinite gave me headaches within 15 minutes.
And watching any Let's Play of a shooter gives me headaches within a minute.
I've chalked the majority of it up to getting older. My gaming binges used to also give me headaches, but only after several hours. So I've had to switch to strategy games instead. But still, something about certain ways things are rendered or the FoV or framerate is affecting me and I wish I knew what it is.
Portal, like many new-ish 3D games, have a very narrow FOV (in the 60-75 degree range) compared to classic 3D games (90-100). If you have a widescreen monitor (which amazingly wasn't standard when HL2 and Portal were released) try cl_fov 110 in the console.
I hope more research is done on this, and some solutions are found, because I really want to finish playing Portal. :)