In Wrath of the Lich King, as you were leveling up and making your way through the content, the Lich King was everywhere. You learned who he was, what he did, what he was doing, and in general just to really, really hate this guy. He popped in up numerous quests, zones, lore, dungeons, the guy had a more active PR department than Lady Gaga. They learned a lot from the mistakes of Burning Crusade, where you didn't really learn anything about this Illidan dude who was supposed to be all big and bad.
In Cataclysm, they have departed from that. Sure, Deathwing makes the world explode, and of course, people are kinda upset about it, but you rarely ever see the dude. Sure he randomly flies overhead and lights things on fire, and yeah he appears in like one maelstrom quest and one twilight highlands quest, but they did a really, really terrible job of describing who the heck this dragon is, why he's so pissed off, and what his goals are. He's just... well... angry.
The Alexstrazsa/Deathwing quest scene in TH shows of the potential this story could have had, but they stopped well short of what they should have done. Something about elementals being restless, some name mentions by random worshippers, but not much other than that.
If the Lich King was Michael Jackson, Deathwing is Tito.
And Tito is pissed.