From Ars Technica: Eight years in the making: Blizzard unveils Diablo III
So far, two player classes have been revealed: the Barbarian and the Witch Doctor. As in Diablo 2, the Barbarian fills the role of basher, using weapons and might over spells to wade through hordes of enemies. The first new class, Witch Doctor, brings to the table a collection of fire spells, curses, mind-control spells, life-draining abilities, and controllable pets. Though speculation is running wild about which other classes will make the cut, many are looking back at Diablo 2 for hints. The original starting line-up for Diablo II was Amazon, Barbarian, Sorceress, Necromancer, and Paladin.
In addition to a brand-new story and as-yet-unrevealed new player classes, known improvements for Diablo III so far confirmed include a Havok-powered physics engine for object and cloth dynamics, as well as water and ragdoll, more side quests including class-specific quests, improved random dungeon creation, class-specific gear with class-unique art, gendered versions of each class, ...
I know it's a little thing, but reading that there'd be gendered versions of each class made me really happy. The Witch Doctor sounds like a cross between the necromancer and the druid. The ability to make a female barbarian makes the amazon -- the token female warrior -- a little less "necessary". However, she was the ranged fighter; I assume that gameplay element will be represented. I also assume they will have some kind of elemental spellcaster.
I love story-driven RPGs, I sometimes roll my eyes at "action" RPGs, and I prefer 3D games. But Diablo 2 has a crack-like quality to it. Mr. Entity and I still play it from time to time. I hope they don't screw up the formula.
The official site has a rather extensive gameplay demo.