In Diablo 3 there will be five character classes, like in Diablo 2 for choice.
Two classes are already introduced.
First there is the barbarian, this muscular warrior is already well known from Diablo 2.
And there is the new witchdoktor, some may notice similarities to the necromancer class from Diablo 2.
The other three character classes are yet not known, and Lead Designer Jay Wilson said, that it isn’t yet decided, which character classes will be implemented for the start of Diablo 3.
Below you will find some details concerning the barbarian and witchdoktor, but before that lets summarize some general informations about the character classes in Diablo 3.

First of all, there will be free choice of the gender.
Players will now have the option to smash hellish forces with Mr. or Mrs. Witchdoktor.
No more male Druids only and the magical circle of Sanctuary will not be consisting only of sorceresses anymore.
Finally gender equality also conquers computer games.

There will be a broad spectrum of new skills and abilities available, with impressive sound and graphical effects, to give the player the feeling of playing a very strong character with great power.
The characters will differ strongly from each other, concerning skills and tactics, even more than we know from Diablo 2.
The use of the right tactic against different hellish forces will be the main key to success or defeat.

It is to be expected, that Diablo 3 will not start with all the “old” characterclasses from Diablo 2. Which class will make it to Diablo 3 besides the barbarian? We think, that at least one of the old classes will make it to Diablo 3.

Blizzard focus also more on story and quests, than in Diablo 1 & 2, and a new feature will be monologues heard from the character, while exploring the world of sanctuary, to allow an intense characterdevelopment.

Detailed informations about the barbarian and the witchdoctor:

The Barbarian:

The homelands of the barbarians is the northern part of Sanctuary, where light blue icy landscapes were softly bedded in the cold white snow.
The nature of the barbarians is as rough and untamed, like the wilderness of these lands, but the barbarian is no brainless slaughterer, like they were used to be seen from the southern inhabitants of Sanctuary.
The culture of the barbarians is far more complex and sophisticated than anyone can even imagine, and the motives for barbarian actions are often misunderstood by foreigners.

The barbarians guarded these lands since ever, and their holy mission was the protection of the worldstone, that lied deep within Mount Arreat. It were the barbarians who fought against Baal and his minions, and thousands of these brave and selfless warriors died, while defending the worldstone. But they have failed. Even the sacrifice of these courageous souls could not stop Baal from corrupting this holy relic.

What cruel destiny for a nation of warriors dedicated to only one mission: the protection of Mount Arreat.

After the destruction of the Worldstone, leaving only a crater, where once the mighty Summit of Arreat was located, the barbarians disappeared.
No one knows, where the barbarians have gone, or how many of them survived, alive with the shame of defeat.

General:

The barbarian class will be available in Diablo 3, and as we know from Diablo 2, this huge, muscular warriors will be able to wear the strongest armor and use the heaviest weapons.
In the gameplay trailer we can see the barbarian using two one-handed axes, and later also a big two-handed hammer.
Whether if it will be possible for barbarian players to use two-handed weapons, one handed, like in Diablo 2 is not revealed yet.

Skills:

Battle Cry:

The barbarian uses this mighty battle cry, to increase the defense of partymembers for a short amount of time.

Cleave:

This massive attack deals a good amount of damage and may cleave the opponents of the barbarian.

Furious Charge:

This attack allows the barbarian to rush very fast to the chosen victim, crushing everything that lies between him and his target. The primary and secondary damage is increased.

Ground Stomp:

This ground attack shakes the earth around the barbarian, leaving the opponents in this area stunned for a short time.

Hammer Of The Ancients:

A strong attack, which increases the physical damage and the chance of critical hits.

Leap:

A jump attack, which does moderate damage and gives the barbarian the ability to jump over obstacles, like broken bridges.

Seismic Slam:

Also a ground attack, which starts an arc of shaken earth. This shockwave knocks off every target, and destroys objects in its way.

Whirlwind:

This skill is already known from Diablo 2, and seems to have the same effects, although it has a better optical look.
The barbarian circles around to hit every opponent in range. Depending on the skill level, the damage is increased.