More GPIO pins. The GPIO header has grown to 40 pins, while retaining the same pinout for the first 26 pins as the Model A and B.
More USB ports. It comes with 4 USB 2.0 ports, compared to 2 on the Model B, and better hotplug and overcurrent behaviour.
Micro SD. The old friction-fit SD card socket has been replaced with a much nicer push-push micro SD version.
100 Base Ethernet (same as the original Model B)
Lower power consumption. By replacing linear regulators with switching ones we’ve reduced power consumption by between 0.5W and 1W.
Better audio. The audio circuit incorporates a dedicated low-noise power supply.
Neater form factor. We’ve aligned the USB connectors with the board edge, moved composite video onto the 3.5mm jack, and added four squarely-placed mounting holes.