Cataclysm could of been an awesome expansion if they used the world more but they didn't. They left all the end game content to the level 80 zones. The whole world changed. They should of used this more to make more world quests and massive world events.
I also hated DS being out for way too long. The content got stale and they had nothing for players to do. Most players completed the insane achievement in this time because they were that bored with the content.
They did learn in MOP to make content last for longer. A lot of things are being dragged out like reputation and cooking with the tillers etc so people don't breeze through the content. I have to hand it to Blizzard, this has worked great. It's now 2 months into the expansion and I am still doing things in the game.
The things I don't like about MOP is the level cap. Another 5 levels is bullshit. They made it only 5 levels last expansion because they were updating the old world and only did 5 levels. MOP is a new expansion so it should of had 10 levels, if not 15 to make it level 100.
I also don't like the world pvp aspect. I remember Blizzard giving people purpose to attack world cities and to create world pvp. There is nothing like that in MOP. This expansion is based on war - where is the war?