The content drops on June 25th, and the Druid will be available as a premium playable class (and free to VIPs). The Druid is primarily a caster, but he's also proficient with daggers, sickles, staves, and clubs. His signature ability allows him to transform into a winter wolf, a dire bear, a water elemental, or a fire elemental. Each shape has its own set of spells, and the class also features a Druidic oath that boosts resistances to entanglement, poison, and other natural ailments.
More info on the expansion is available via Turbine's official website.
[Source: Turbine press release]