The Horde (right) here is about to face of with the Night Elves. They're lead by a Troll Shadow, and a Far Seer, who's identified by the Spirit Wyvern that he rides. The pyrotechnics we see near the Night Elf assassin is a lightning bolt, launched by the deadly aerial mage. The rest of the Horde army basically consists of mercenaries, kobolds in the front and Gnolls in the back.

The opposing Night Elves have a the advantage, lead by a Priestess of the Moon (The Big Owl in the center). Above her are two Priests of the Talon, while hovering behind are four Hippogriffs. The Night Elf Assassin is selected, we get the first look at her portrait.

You'll notice that all the units a generally much smaller in this screenshot than in those from a prior build. This is due to the fact that Blizzard has recently implemented a zoom feature with three levels of zoom. Here we see a screenshot at the minimum Zoom level.