The Samsung Galaxy S4's largest physical change is its display, a 5-inch monster (up from 4.8 inches on the Galaxy S3), with an improved screen resolution and pixel density.
Despite being a bit taller and wider than the Galaxy S3, the Galaxy S4 is thinner and weighs three grams less, at 130 grams. The rear camera, too, has been upgraded, from 8 megapixels to 13 megapixels.
The Galaxy S4 will run Android 4.2.2 "Jelly Bean," with Samsung's familiar TouchWiz skin loaded on top.
You can see full specs for the Galaxy S4 here.