Instances in the Burning Crusade are different from the ones live in that they are all divided into multiple wings. This is a welcome change, as being stuck in an instance for hours isn’t everyone’s idea of a good time, especially when you have limited time to play.
While doing some of the Outland instances may take as long or even longer to complete when you combine all of the wings, the individual wings are all very manageable and don’t take too long to do. (unless ofcourse you are in a disaster of a group) A big change to instances is the ability to crank their difficulty up, this is done to provide level 70 players with a reason to head back to previously visited instances. The mobs in a heroic instance are higher level, hit harder and have more life but drop better loot. The bosses in a heroic instance drop special tokens for the group, which can be turned in for heroic loot in Shattrath. And last but not least, killing in heroic mode instances will provide reputation gains up to exalted.