Compared to the Model B it has:

• 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.