Easier to use, touchscreen technology. And much more important (for Apple): it syncs your iTunes contents plus many more data.
Ah! By the way... It runs MacOS X and it's not brown.
Photo from: http://www.tuaw.com/
ps: He's right, it usually takes me more than 3 months to fully understand my cell phones. And it's quite frustrating don't being able to change the fonction of the buttons.