The first manga story line he wrote about Warcraft revolved around the events leading up to patch 2.4 in the Sunwell Plateau. I picked up all three of the books in a archived version over Christmas, and it was quite a good read. I'm definitely looking forward to picking this one up, and according to a Blizzplanet page, the release date is scheduled for August 1st, 2008.
The artwork pictured to the right (click for a higher resolution image) looks pretty cool, and appears to be an Orc Rogue. Since the book is called Legends, we can assume it's about some legendary figures in Warcraft. I would take a wild guess that the Orc pictured is Thrall, but I could be wrong, and feel free to disagree with me.