So, I've had about a week with the Gear VR. Still zero motion sickness. I've even been playing one game that is a space ship dog fighter where you spin enough to make me occasionally dizzy. But after a second I regain my sense of stability and go on.
I believe the key is to be sitting down in a stable chair or couch. I tried a swivel chair very shortly and felt less comfortable that way although I did not play long enough to get motion sickness that way. But it felt noticeably different.
The only possibility I see other than a stable seat would be quality of motion tracking, but I don't think that is the primary issue.
One thing I noticed when I let someone else play it was that he chose to play it standing up and he was swaying around like he'd downed a quart of Jose Quervo. It was pretty obvious that his brain was getting mixed signals. His eyes were telling him one thing and his muscles were telling him something entirely different. We have a tendency to believe our eyes, yet in this case that was the problem.
At least with current VR technology, I believe standing is the cause of the problem and VR games will induce sickness if they do not avoid this. When firmly seated, there's nothing for the brain to get confused about and any time the eyes try to trick the brain, the muscles send the signal that everything is a-okay because you are firmly planted. Worse comes to worse you fall over on the soft couch. With the arm rest you can only fall one way. I attribute this to the reason that I seem to be able to spend countless hours in VR spinning wildly even to the point of being dizzy and experience no sickness. There could be a link to motion tracking, but I don't think the motion tracking on the Gear VR is that great. It's reasonably good, but it constantly drifts. It's probably good enough as long as you can constantly reset it. Some games allow you to reset the motion tracking inherently while others require you to leave the game to reset the unit. Usually, it is the supposedly uncomfortable standard games like MineCraft that are always inherently resetting the motion tracking. When the thumb controller is what turns you around rather than your head, you are constantly resetting the tracking without realizing it. It for the most part only has problems on the horizontal plane and seems to correct itself on pitch well enough most of the time. I think that the problem on the horizontal plane with yaw is that it's picking a fairly arbitrary point to be "forward". Pitch may be defined more accurately according to gravity, giving you a consistent "down".
VR is not meant for standing. True VR involves paralysis and is a technology probably 1,000 years in to the future, but at least a century or more. This should not be confused for that. This is basically just true 3D gaming. As such, it should be played like it's always been played: on a couch with a controller in your hand. As long as the technology tries to be something it's not, it's going to have problems. The sooner it can embrace what it actually is, the sooner it can catch on.
These companies like HTC that are making VR games where you stand are just asking for a law suit. It's only a matter of time before someone trips and is seriously injured. It's inherently unsafe, although many of us may be willing to take the risk. You're blind folding yourself and lying to your brain to tell it you can see and filling it full of ideas about things being around you that are not there while being totally oblivious to things that are not there. Moving around blindfolded with this kind of false information is asking for all kinds of problems.
In our overly litigious society, I don't see how everything else has to have a warning label on it, and yet this has managed to get past the lawyers. If it were like the rest of society it would start the game by saying, "You agree to use this unit sitting down in a stable seat and never to stand up while wearing this unit. Standing while wearing the unit is inherently unsafe and not at all the intended use of this product. Users wear this unit at their own risk and the company assumes no liability for the incorrect use of this product." You'll probably see these warning after the first law suit hits the courts. I would be tempted to start every game with it asking if the user is seated firmly in a stable couch or chair and exit the game until the answer is yes.
One game had a post that I almost wanted to grab for stability, except in the real world there was nothing there to grab. If I had of relied on that standing up, I would have fallen as I tried to catch my fall on a non-existent object. Even assuming that it tracks you to keep you in a safe area, it's just a matter of time before someone comes into that space unexpectedly and you trip over the baby or the dog and face plant. Besides, very few games can be fun and limit you to staying in a small area. And teleporting from one area to the next is un-natural and seriously fun draining as well.
Yet, if you just play it like any other game - sitting down on a couch with a game controller - you can play it just like any other game with next to zero risk of breaking any bones and from an infinitely more stable and less nauseating platform. This is not true VR; your sense of smell, taste, touch, and balance are not something that it can control, and if it could you would be paralyzed and unable to stand up anyway. What it really is is just a better video game monitor and that's it. I think the sooner we embrace that, the sooner we can start enjoying games for it.