Marksmen hunter looks pretty powerful. It has one shot potential ,and can have crazy range from its mastery. Definitely possible to kill other ranged before they even get close enough to attack you.
Rogue as usual is probably pretty good too. One shots out of stealth as always.
Healers seem powerful as well. Holy paladin hits hard and is unkillable. I assume disc priest is strong as well although I have not messed with it. Restro sham hits unexpectedly hard due to having a +40% damage modifier on lava burst(and other damage spells) so they are worth looking at as well.
Frost DK seems kind of good. They have everything they need by 20, and that chains of ice talent is really juicy. It gives a 214% attack modifier on a ranged slow that scales with mastery. The self healing is weak though so it falls behind some of the other specs in my opinion.
From what I have seen the bracket is pretty forgiving this time around with most specs having something worth playing