This isn't a full post yet, but I'll come back and edit it into something real once I get my thoughts in order.
From reading all of the previews, it looks like we're getting a lot of new mechanics to control each encounter. We get speed buffs, artificial LOS mechanics, landmines, walls of fog, and other stuff.
My takeaway is that the old crowd control ("CC") of vanilla and Burning Crusade isn't coming back. In the good old days, it was simple. If you pulled a pack of mobs, you would try to root/sap/hibernate/freeze/sleep/hammer all but one of them, and then focus on them one at a time. Only one mob (in a perfect world) was allowed to be active at a time. It was effective, but it was very, very simple.
I think Blizzard may have decided it was too simple. The Cataclysm picture that's emerging is one of more fluid crowd management ("CM"). Mobs coming in certain directions can be slowed or damage. Certain casters can be avoided by ducking into clouds of smoke or taking cover under camouflage. This is more interesting, and will likely require more skill, than simply sapping all the mobs and hitting them one at a time. It also fits into PvP better, especially the rated battlegrounds (Arenas will be a little too small to see these abilities used to their full effects, I think).
I'll go through the preview abilities I think are related to this in a few days, and explain how I think they all fit together.
An update from me and closing my guides
5 days ago