The new phones have improved the already-great camera by adding super-resolution technology, that uses multiple pics stitched together, similar to HDR. Video-wise, 1080p slow motion is now in your pocket, and the FaceTime camera is improved.
You'll also get NFC abilities, enabling you to pay with your phone at a ton of business that are signing on. To make all this possible, Apple tossed in a faster A8 processor, so that shiny new iOS 8 should run without a hitch, even at higher frame-rates. There's also a barometer that can measure relative elevation, which works in conjunction to another processor, the M8, to give you better health tracking abilities for physical activity.