Per the review I linked to, the changes are:
* Uses a 6 Megapixel CCD (instead of 5MP)
* New ISO range of 80 - 800 (instead of 50 - 400); lower noise than previous sensor
* 2" LCD display (versus 1.8")
* Live histogram in record mode
* New widescreen (16:9) still image mode
* New Sports scene mode
* Black-colored body; slightly larger and heavier than S2