Class abilities were reworked dramatically across the board, with some still needing a serious balance pass. That left many players not only feeling underpowered, but having to learn how to play their characters all over again. Bosses in large-group raid dungeons that were easily killed each week by experienced guilds of players suddenly became challenging again, or worse, completely unkillable, halting forward momentum on old content for a good chunk of the high-end player base.
Some people have made arguments that quest blues can sometimes be more powerful than heirlooms, especially with sockets. I'm not convinced. The simple fact that you never have to even look at quest rewards will save a non-insignificant amount of time over the course of leveling. Also of consideration is the value of enchanted gear never having to be re-enchanted.
This week, the story began: A short series of quests begin to pit Alliance and Horde against each other, and the skirmishes over territory that will soon be destroyed began. Realistically, that meant players had about 20-30 minutes of questing, at which point (without any in-game announcement or breadcrumbs) four world quests opened up in an existing contested zone.