iPhone 6S and iPhone 6S Plus come this year with 3D Touch technology, which involves the use of a Taptic Engine to record various types of presses and provide tactile feedback for actions, these functions also exist in the Apple Watch.
Separately, Apple has created a more resistant front panel that it calls Ion-X, but in reality we are most likely talking about a Gorilla Glass 4, and this is because Apple mentions Corning as one of the partners it worked with to implement 3D Touch.
Apart from 3D Touch and Taptic Engine, Apple has not implemented any other innovation for Retina HD screens, they keep their diagonals, resolutions and number of pixels per inch, along with all other features.
From the contract to the brightness or the angles from which the images can be seen, the Retina HD screens of the iPhone 6S and iPhone 6S Plus do not bring major changes for Apple's smartphones, and this was to be expected.
