1) It's really tough
2) It requires lots and lots of practice and player-skill unlike any previous encounter.
3) It's really, really tough
It's looking more and more like the guilds who have killed him have done so using some sort of LoS trickery. We refuse to take advantage of any exploits like that, so we have been unable to make the sort of progress they have. However, if it turns out that they did actually somehow do it legitmately, then hats off to them.
We are still in the process of learning the fight, and it's really, really tough.