It would be an understatement of epic proportions if I were to tell you that this is an aggro-sensitive fight. It goes far beyond that. O'mrogg is immune to Taunt (not just the Warrior's taunt, all forms), dumps aggro frequently, hits hard, blastwaves your whole group, and drops AoE fear-bombs for added fun.
There are two methods to conquer his madness. You can deal with the fight slowly, meaning everything is carefully controlled, the tank is given a really long introduction for aggro-building, and DPS is gentle. You might find, though, that with the aggro dump and random attacks that slower may not be better. Most of the time, success results when everyone forgets about the aggro table and tries to kill the jerk as fast as possible. It may be beneficial to mind your threat when the fight begins, before the first aggro-dump. Let the tank build for a few seconds, then lay into him. Whenever the DPS feels they have a good opportunity, they should lay into him with everything they have. It is better for O'mrogg to chase a DPS class than for him to chase a healer - and trust me, he will pretty much always be chasing somebody. Complete threat drops work for the targeted player as well. If you need to drop him back onto the tank (or the overzealous DPS), Vanish, Iceblock, Feign Death, Hand of Protection and Divine Shield are entirely effective. The main things you should remember are to attempt to stay out of range of Blast Nova, keep anti-fear effects on the tank, (Deathwish, Fear Ward, Tremor Totem) and be prepared to drop aggro. Other than that, its a pretty fun fight.
