Recently camera manufacturers focussed (pun intended) on the quality of sensors giving us better detail in shadows and highlights and the ability to photograph in ridiculously low light without flash.
Not all pixels are created equal. Cram too many pixels in a small sensor and the quality eventually decreases as noise overtakes resolution. There is a point where sensor wells are too small to capture the red part of the light spectrum. Engineers have made huge advances that seem to go against this theoretical limit to the number of pixels in a sensor.
But then theory was thrown out the window with the Lytro camera where the user chooses what to focus on after capturing the image.