From Diablo Wiki
Character customization is a big part of all modern RPGs, and Diablo III is no exception. Characters in D3 will differ by their skills, the runes they socket into their skills, and their choices from the vast pool of possible items of equipment. All characters can also be played as a male or female, unlike the single gender of each that was available in D1 and D2.
A quick list:
- Skills are the most obvious form of customizing, and with more than 50 skills each for the Barbarian, Witch Doctor, and Wizard, divided into three trees, there will be many different viable builds for each character class.
- Skill Runes add to the variety, since even if two Barbarians have identical skills, the runes they choose to socket in those skills will make them function differently.
- Items. Equipment options in Diablo III will dwarf even the almost countless item choices in Diablo II.
- Gender. Each character can be played as a male or female, with entirely different artwork for each.
There is no character customization in Diablo III, in terms of facial features, facial hair, hair color, height/girth, etc. The D3 Team experimented with that sort of thing early in the development process, but rejected it after some experimentation. They reported that it was fun to play around with the creation screen, but that testers would spend several minutes making their own character, only to start playing and find that 1) their character was too small for facial features to show up, and 2) face and hair were immediately hidden by a helm or huge shoulder pads.
The way to make a character look different in Diablo III is to wear unusual armor or wield a cool weapon. After all, the game is about finding great gear, not playing with skin tone/height/hair color sliders in a character menu.