Its not often that I have to admit I'm wrong...okay I'm married so it happens a lot. Its not often that I want to admit I'm wrong. I judged Cataclysm as the straw that would break WoW's dominance over the MMO world and shatter the game (poetically as Deathwing shattered its world). However, the sheer competence with which its been implemented crushed that prediction to dust.
The game is very solid. Fewer breadcrumb quests, and a Warchief's command board to host most of them leave characters knowing where to go. Quest chains lead into one another, and unless you outlevel them, will take you through the whole zone. The xp requirements have been lowered again, and most class mechanics simplified. All in all its a game that is infinitely easier than previous versions of WoW mechanically. That and the redesign of Azeroth and the sheer level of detail for some parts of it is an amazing example of how to do this kind of example.
But this game is not the WoW I purchased years ago and that I've enjoyed. For me as a player it is too easy. I've heard that heroics and raids are hard, but I've also heard that before as well (and usually its not a mechanical difficulty its a difficulty of numbers, and better gear will make them laughable.) Is this game breaking? Well, its the same thing that WOTLK did but to a larger scale. WOTLK didn't break the back of this game, and so Cataclysm will not. What I do think will happen is many of the more serious gamers will leave WoW, maybe just until the next expansion, after getting any number of characters to 85 (the only 'difficult" part being the break between 60-80 where you have to go through the "old" content).
The other thing I dislike about this new WoW is the requirements to complete all quests to advance. If you don't want to do a quest or can't figure it out, chances are you're fucked for finishing that zone. While this isn't as much of a problem for the 1-60 zones (there are always other zones or other ways to level) it becomes a large problem for 80-85. Sure you can level through to 85 by other means without touching a quest, but if you do you will still probably have to do the quests to unlock instances and the like (similar to how you have to discover the throne of tides to even do those instances).
The other thing I dislike about WoW is the massive stat inflation, a fact made even worse by Cataclysm. The difference between a lvl 60 in vanilla gear and a lvl 60 in TBC random greens was several thousand HP. For TBC 70 to WOTLK green 70 it expanded to 5-10k hp. Cata is harder to gauge since the whole stat system changed, but pre-heroic tanks hit 100k hp easy, especially feral tanks. I understand its all numbers, but its just gotten so far out of hand. Most of my friends who are still playing WoW disagree with me about this, but its how I feel.
Now for some honesty about my experiences with Cataclysm: I did indeed play before the release to experiment with the new gameplay mechanics. I have played every class (getting Rogue, DK, Hunter, Priest and Paladin to 85) post-Cataclysm. I am very pleased with the changes to Hunter and Warlock's game mechanics, and like many of the overall changes. I even like the reduced number of spells and abilities for each class, and the fact that you don't have to buy each rank of them. I also like that they gain in power as you level. The lore level of the quests has improved greatly. The game, however, does not hold my interest. With vanilla especially, and TBC and even WOTLK, I was driven to do more, to experience more, to see more of the game. I do not feel that drive in Cataclysm. In fact, there are so few quests that while they send you over the whole zone, there's little involvement in the game itself. I also disapprove of the massive overuse of phased content (one part actually is bugged to the point that you have to stand exactly in one specific spot to talk to an NPC to turn in a quest....like I said before being unable to complete this quests prevents you from advancing in this zone.).
Overall I think the expansion is a solid one, but I would almost have preferred it to be a separate game. I'm certain now that WoW will be around for a very long time, and probably will have several more expansions as WOTLK and TBC content need to be cataclysmed.