There are a few problem categories but none of them are "definitive":
"Flicker". This encapsulates PWM, FRC, and a few other scenarios. I think this is the biggest problem for the most people.
"Focal and Display Tech Issues". This covers new screen materials, font anti-aliasing, pixel patterns, subpixel rendering.
"Blue Light". This covers the actual light (intensity, bandwidth) output by screens.
While I think we are all sensitive to blue light (it's not natural), I find that MOST people are having issues with flicker in one form or another.