The jump from Wrath to Cataclysm solo content is remarkable. The new zones contain some of WoW's highest production values yet, with spectacular scenery, occasional fully voiced in-game cut scenes, and more bells and whistles than even Northrend had to offer. (For instance, someone took the time to make a specific animation for players bounding along the sea floor in the undersea zone of Vashj'ir.) However, this increased focus on story comes with a price in terms of flexibility - progression across zones is highly linear, with access to each phased quest hub gated by doing all the quests before it in precisely the correct order.
The other thing that is really remarkable is the jump in difficulty. Mob HP more than doubles between the level 80 quests of Icecrown and the level 80 quests in the new zones, and I've seen level 84 solo mobs with more than 50K HP (compared to maybe 12K at level 80). The jump is so pronounced that Blizzard felt compelled to remove 90% of the exp for characters who try to remain in old expansions beyond the respective level caps to keep players from hiding in Northrend until they gain some levels. (I'm not thrilled with this change, as it basically kicks players out of about half a dozen zones.)
With increased difficulty comes increased rewards. Quest reward item levels jump by 100 ilvls between level 80 quests in Icecrown and Hyjal, and the very first green quest rewards replace all but the very best gear available in Wrath's five-man content (and all but its final raid).
Finally, the Cataclysm approach comes with an obvious cost in terms of quantity. I gained a level in about four hours last night without either heirlooms (Wrath heirlooms don't work past level 80) or rested exp, despite spending some time screwing around with Archeology. The exp curve does jump from there, and some of the new zones are actually pretty large, but the odds that I fail to reach level 85 by the end of the year are not looking good. Worse, many of the quests seem to be handed out by neutral faction questgivers, limiting the amount of variety I will have to look forward to on my horde characters.
At the end of the day, Blizzard has really focused its efforts on perfecting its style of questing, even if this means exaggerating the drawbacks of this type of experience. Many players don't like it (and presumably many more do), but if nothing else the game is recognizing and sticking to its strengths.