As I'm sure all of you have heard the gear in BC makes everything currently in wow obsolete almost immediately.
The gear is also more smartly designed. Gone are the days where a mage has agility and a warrior has spirit.
All of the theroycraft is centering around what it's going to be like at level 70. Most are assuming if they have +500 spell damage now they will have +1000 at 70. Based on what I've been able to find this is wrong.
Blizzard's approach to gear seems to be this: For armor take what you have now and add gobs of stamina. If your class's current uber gear is a ring with 10 stamina 20 agility and +1 crit the at level 70 it will be 30 stamina 20 agility and +1 crit. If it's a helm with 5 stamina, 30 int and 20 spell damage the level 70 version will be 40 stamina, 30 int and 20 spell damage. And so on. Weapons do scale up the damage and you can expect your level 70 weapon to contribute twice as much damage as your level 60 one does.
Additionally the healer gear almost always comes with mana regen, while nuker gear does not. The good news is generally you'll see +healing and +all spells about the same so +healing isnt massively outpacing dps.
So what can you expect for your level 70 gear? Everyone will have around 8-9k hit points. Even mages and priests. Warriors and locks will probably have 10k. This means fights will be much more tactical. You will either have to focus fire or it will become a battle of attrition. No longer will pvp be a bunch of 1 v 1s.
Mages -- Already the masters of downtime BC is a disaster for mages. Mages rely on quick kills and burst dps. Everyone has triple the hit points, but mages have the same mana pool and only do 50% more damage.
Warriors -- Also of note is that I didnt see ANY dps warrior gear. It's all tanking gear. The good news is that mortal strike is no longer a joke. With all the longer battles it will be very useful to burn down an enemy. The bad news is blizz is trying to force warriors to fight with sword and shield.
Hunters -- Probably the class least effected by BC. RAP nerf means you wont have the dps you did, but pets are stronger to partially make up for it.
Rogues -- Congratulations, you are a fury warrior. Stunlocking is impossible as is 2 shotting with ambushes. The clothies rejoice. The good news is all other dps classes have been nerfed, you are now the only sustained high dps class.
Warlocks -- Affliction is your new best friend. Longer battles mean your dots will actually be able to tick to completion.
Healers -- Already the most important class on the field healers just got more important because it's much harder to CC anyone or dps someone down before you can get a heal off.
Note: This is based off what little I've seen for level 70 purples and they are subject to change. As always I dont care about pve.