I see a pattern ^.^
When WoW TBC was drawing near, everyone was super excited, mostly because Classic WoW was such a great experience. That's just what people felt at the time. Hey I wasn't even a part of any 40man raid, PvE was hard to do, but still the game was deemed as fun.
Than TBC came which really hit the jackpot. Sure it was not all that innovative, all it did was bring Arenas, everything else was just to make it more casual and the old "new talents, more levels, new areas" etc. Personally I remember having tons of fun, it was so cool. Ofc I was biased as my favorite characters were Illidan, Kael and Vashj. At the time I was one of those people who said "how can there be Blood Elves at Horde??". Eitherway, even if it was unbalanced, I still think it was the best expansion with the best boss fights ever and the best dungeon ever.
Than WotLK was announced. People thought it would be this revolutionizing expansion. That it will be better by leagues than TBC that it will be just as cool as Classic WoW if not even cooler. It actually produced a lot of disappointment to the players. It's really when the playerbase changed, the old veterans quit, felt the game didn't cater to them at all anymore, and new players arose, those who wanted to play WOW because it was the most popular mmorpg for some time now. People who felt they are entitled to win the game because they pay 15$ per month. Other than better looking terrain and Quests System, I feel like WotLK didn't bring much to the table. All in all WotLK was a farm fest, changed completely the notion of raiding. If before raiding was a threshold to achieve in WOW, in WotLK it became as casual as 5mans.
Than Cataclysm was announced, it will bring back content for old veterans. And you know what, it did... the 5man dungeons were actually hard. I haven't had so much fun with 5 man dungeons ever, not even in TBC. But you know what? Catering to the old veterans (who didn't return in the numbers they expected, as many just quit the entire genre all together) made the new entitled casual guys scream loud and cancel their subscription. And you know what? It worked! Mid-expansion, Blizzard throws in a tool which tells you how to solve the boss fights, although they said they wouldn't do that. Raiding became as casual as it ever been, everyone could do it, it was no harder than frying two eggs in a pan. From where I felt that fights were spectacular and tactical in Classic & TBC, they turned into dynamic and gimmicky. I remember Ragnaros fight being impressive, but fighting Deathwing was.... what the hell was that. Cataclysm became even more of a let down than WotLK. It was the expansion in which it was clear that there were two different camps in the playerbase, the hardcore players and the casual entitled. The casual entitled do bring much more money to Blizzard, so eventually they got catered too.
However, eversince WotLK, the number of subscribers has dropped. Blizzard realized that the NA and European markets provide less money from WOW than the Asian market. So now Blizzard decided to cater to the asians, they brought in Pandaren and Pokemon. It's not pure coincidence, it's not the fact that Blizzard love their franchise, it's not about Pandaren making the game better, it's about making WoW a cultural interest for asians. That's why there are so many asian themes in this expansion. Not just the architecture, but the black souls, the art of the lion-men race, the giant turtle which hosts an island on it's back, all that stuff is there not to make the game good, but to appease the Asian market.
Now I will admit that the new talent system in MOP is actually cool. And I also admit that it's nice to not have a supreme evil bad guy who has a plan to end the world and needs his ass kicked.
But seriously... MoP might not disappoint as much, because Cata disappointed the most and for good, you know? Like I don't expect to like MoP. I expected lots of stuff from Cata, but I don't expect anything from MoP, because I know where Blizzards interest lies. It doesn't lie in me, they don't want me to have a good time, they want the asian kid to have a good time. They don't want my enjoyment, they want the asian kid's money.
I really feel like the game just lost it's purpose, it's identity. In Classic and TBC, I felt it was the game in which you did what you wanted to do. In Classic I didn't even raid, I was just happy leveling and exploring. And for a good time it was what I enjoyed in TBC too. Than in TBC I started raiding. Raiding was fun, especially Karazhan. It felt like an open world, a real open world.
With the introduction of Achievements and instant teleport to instance system, I feel like the capital city is the main menu, and than everything else is instanced and not part of the same whole, of the same world.
I expect MoP to disappoint too, if there are still people to disappoint. I expect it to be a huge letdown, especially for the old Blizzard fanbase. Just like SC2 story and D3 are.