Big announcements (at events like BlizzCon) about expansions (like Wrath of the Lich King) always bring up the question of whether the planned updates to the game are any good or not. If it were just a regular patch people might complain about a particular buff or nerf, or lament that they have no chance or desire to see a particular new dungeon, but no one would expect a mere patch to totally revolutionize the MMO genre.
Expansions though, for some people, are supposed to be the thing that doesn't just expand the game, but changes the face of the entire gaming world. "More of the same" is just not good enough for them. But as much as I, too, would love to see more innovation in MMO gaming, and even World of Warcraft in particular, I have to tell you, folks, Blizzard is made of mere mortals and some of you may be setting your expectations a bit too high.
No WoW expansion can ever totally revolutionize the MMO genre, because at this point the genre is mostly WoW. While there are, of course, other games out there, WoW is the current MMO superpower, with a population larger than some countries of the world -- it defines the standard upon which to improve. To "revolutionize" the genre, you'd need a different, better game, because for WoW to change too drastically would mean turning the game into something other than what it is: replacing the current game with entirely different mechanics, ways of playing, even reasons for playing altogether. Expecting WoW to become something other than what it is unfair, even if that were to be an improvement, because then it wouldn't be WoW anymore. It could also be a financial disaster to keep the name but change the game, as the fiasco with Star Wars Galaxies proved (read up here to find out how their "revolutionary" New Game Enhancements turned out).