Some additional comments:

Haiyan: You want to stack on meteor, not spread out. If you do not stack in challenge mode, you die. The conflag may be a small AOE, so I think you want to spread for that and then stack for meteor.
Ming: His abilities are on a timer. Ideally you want him dead before Magnetic Field, so I pop everything for Ming.

Gekken: This is where I got stuck in Challenge Mode the other day. For heroic this fight is almost trivial. Supposedly you can interrupt everything, but I just interrupt the cleansing fire from the Oracle. My kill order has always been Oracle, Ironhide, Shivguy, Gekken, and then the Hexxer. The only thing is that you have to be ready to dispel the hexes. IMO, if you could interrupt anything else, I'd interrupt the Shiv. That's brutal damage. The reason that I kept failing in CM was because something ate all my healer's mana. Once I figure that out I believe that I'll be able to do this fight.

Xin: As above, there is a safe zone between the pillars. You want to spread out and ideally stay out of the fire circles, but otherwise I just pop hero at Phase 2. You can also eat his damage cone with the tank, but it's obviously better to avoid. This fight is a good test of whether your healer has enough spirit. Lastly, in heroic you cannot be hit by the blades for very long and survive, so your number 1 priority is to keep an eye on your guys and move them quickly in case they get knocked into knives by an axe.