They appear to be ghost birds of some sort; translucent and blue.
My rogue just had a failed PUG in there, and I decided to look at the scenery a bit. It's quite an amazing zone. Visually, and by story. It's tells of the Nerubians, how they fled the Scourge by digging, and went too deep. The faceless ones are down there.
It looks great, the story is familiar but new: a three way war between Scourge, Old Gods, and Nerubians. But I don't like it very much. I don't know why not. The pulls aren't especially hard. I actually enjoy the spell flingers, a chance to put my silencing shield throw to good use. I love the last boss; the insanity mechanic is awesome.
Why don't I like Ahn'Kahet?
Accuracy and reverting to the mean
1 hour ago