Apple's decision to transition from the fat third-generation iPod nano to the new svelte fourth-generation iPod nano must have been an easy one. The latest version has the same size screen (just rotated vertically) and the same video support as before, but adds a much more comfortable (sorta) oval shape, a curved screen, an accelerometer, a 16GB version and most importantly, a much improved user interface that aims to solve some of the limitations the Clickwheel has compared to the iPod Touch and iPhone UIs. This evolution succeeds beautifully.

http://gizmodo.com/5047578/ipod-nano-review