Blizzard describes the five types of The Fallen Ones.

The Fallen Ones have a master ... Azmodan the Lord of Sin, one of the Lesser of the Seven Great Evils of the Burning Hells. There are five types of Fallen Ones:

• Imps - These are the commonest of the fallen family of demons. They are the stereotypical fallen ones in look and behavior: small, red, swarming, bloodthirsty, and cowardly.
• Shaman - Fallen shaman priests lead camps of fallen. I have also heard it rumored that they possess the ability to raise imps from the dead!
• Lunatic - These enraged, oversized fallen creatures are bloated seemingly to the point of bursting, an impression buttressed by the fact that these insane demons rush their intended victims and then stab themselves until they explode. A more fitting name could not be found for these maniacal beings.
• Overseer - The fallen overseer drives his smaller impish charges into a frenzy with his ape-like leaping and growling. An overseer among a group of fallen is a dangerous thing, as the cowardice that usually characterizes them is overwhelmed by fear of their much larger brethren.
• Hounds - These slobbering abominations are commonly found among groups of the fallen and are utilized as guard animals, beasts of burden, or even food by their demonic masters. These beasts are loyal to a fault, regardless of the abuse heaped upon them.

They have also released some artwork of the Fallen Ones

More screens were released today, check them out here.