It incorporates a new APS-C-size sensor based on the same X-Trans technology as in the ILC versions of the X series cameras (probably the same 16.3-megapixel sensor as in the X-E1), along with updated image processing.
Fujifilm claims the EXR Processor II and Intelligent Hybrid Autofocus system dramatically improves performance: AF speeds up to 0.08 second, startup time of 0.5 second, and shutter time lag of 0.01 second with a shooting interval time of 0.5 second.
The hybrid viewfinder combines an optical viewfinder (OVF) with an electronic viewfinder (EVF) displaying useful composition information including focus check, exposure, white balance, and depth of field. The X100S allows you to switch between the two.
Fujifilm incorporated the X-Trans sensor technology that originally debuted in Fujifilm's interchangeable-lens models, most recently in the X-E1. To fit in the camera body -- and price segment -- it uses a smaller 2/3-inch version of the sensor, albeit at the same 12-megapixel resolution.
I really hope the switch to the X-Trans sensor eliminates all the awkward interface issues that I had with the X10; the EXR sensors require too many trade-offs when picking shooting modes for optimal results that the X-Trans sensors have overcome.