So for those of us who are not demigods, the intention is that once again, you'll run dungeons to gear up, then run heroics to gear up for raiding, then run normal raids to gear up for heroics. Once you have heroic mode gear, you'll be geared enough to run Sinestra, who will beat you like a rented mule for a few months until the next tier of raiding comes out. So it's a combination of the BC model (run heroics to gear up for Kara -- Gruul and Mags, for instance) and the Wrath model. Well, to be fair, Wrath was also a lot like this at launch.
What's really nice here is the emphasis on badge vendors and crafted gear to help smooth out some of the gaps in gearing up. We all remember The Burning Crusade, when one particular piece of gear could keep you running instances long after you had everything you could possibly want from them (I'm looking right at you, Sun-Eater), so I'm hoping that helps. It's also interesting to note that unlike BC and even early Wrath (Malygos), there's no gating or attunement.
Also interesting is that just because some bosses will drop a half-tier of better loot, that doesn't mean heroic Ragnaros isn't going to beat your face in. I look forward to that, to be honest.
World of Warcraft: Cataclysm will destroy Azeroth as we know it; nothing will be the same! In WoW Insider's Guide to Cataclysm, you can find out everything you need to know about WoW's third expansion (available Dec. 7, 2010), from brand new races to revamped quests and zones. Visit our Cataclysm news category for the most recent posts having to do with the Cataclysm expansion.