It looks like it will be decent- the main challenge will be the huge buffs to certain classes like warlocks that counter what we do. For example, we pop bestial wrath, they put Archimonde's Vengeance on us, which transfers half of the damage the lock takes for the next 10 seconds to you. So I guess you run away during your BW since you'll die if you try to burst down the lock. After that, if you pop readiness and BW again, they can use Dark Bargain, which prevents all damage for 10 seconds and applies half of it to the lock as a weak DOT lasting 20 seconds, which makes them immune to most of our cc. How in the world we're supposed to fight that I don't know.
Shadow priests seem unbeatable as well, and a number of other classes are much harder than on live.
At the same time, getting readiness and other buffs like that is big for us, so I expect BM to be competitive.