Portal was a lot of fun, but it was very good at making me queasy and upsetting my stomach. I imagine it would only be worse to be the main character - in the challenge mode at the end of the game, there should be a challenge to make it through the level without being sick all over oneself. I can't say I liked the timing-critical parts, but the puzzle aspect was quite good. I've played portal before now, but never more than a bit of playing around (and never enough to feel ill).
When I was younger I sometimes got this from visiting Omnitheatres.
Portal felt too easy, but I am not sure how one could make it harder without making it impossible - there were times when I had to think (mostly in the bonus levels), but not *that* deeply.
The downside to Portal sickness is that, like tetris, the puzzles pop back in my mind and even the memory of them is enough to make me feel sick again.
It is potentially just as interesting to imagine what we would design buildings like if we had portals and springshoes as if we had usable wings (which I often daydream about).