The original 3DS and 3DS XL gave me headaches. Whatever they tweaked with the New 3DS XL made it much more manageable because it does some adjustments with face tracking.
The original 3DS was definitely a "hold it at the right angle and keep it there" while the New 3DS tracking allowed for a lot more flexibility with how you hold it for the 3D to not be disorienting.
My problem with my New 3DS XL is that the power button is right where I put my pinky finger when using the shoulder buttons so playing Super Metroid sometimes ends with me "setting the 3DS down" on a desk while playing it, and my pinky bumps the power button which immediately autocloses whatever app you were running. Maybe there's a config option to not do that lol
