In a Pre-E3 presentation, Nintendo President Satoru Iwata revealed an updated Wii U Gamepad, yes, that's its official name. The most obvious change that you can see is the thumbsticks replacing the circle pads which Nintendo believes are more useful for portable devices, but didn't feel right for a games console. The thumbsticks can also be pressed which offers another form of input.
Another much needed change is the back of the controller to maximize the comfort level which really wasn't there in the earlier prototype shown last year at E3 2011.
The controller also features a NFC Reader/Writer which can be used to read cards or figures and teleport them into your gaming experience. The Wii U controller also doubles up as a TV remote, works even when your Wii U is turned off and doesn't hide between your couch cushions due to its size.