What is different between the 5 generation iPod Nano and the 6 generation iPod Nano?

The 5th generation iPod nano has a bigger body, and uses a click wheel (the circle under the screen) to navigate through the iPod. It has a few games, an organiser, a Notes feature, etc.

The 6th generation iPod nano is smaller, square, and sports a multi-touch screen. It has a built in clip at the back.