I personally think MoP is the best expansion yet. That said, a couple of things that I felt was better before:
1) An awesome launch event like WotLK.
I was still lowbie when that happened and though I couldn't really go about unharmed in the major cities for a brief period of time, it was epic and very awesome.
2) The sense of social cohesiveness in-game.
With the advent of 10man and 25man raiding on the same playing field, a lot of people have gone on an exodus from 25man guilds to form up smaller 10man guilds. While every one is entitled to play the mode they wish, I find that 10man raiding guilds are much more vulnerable to break up if one core player has to leave the game. I find there's much less of a community to fall back on in 10man raiding guilds, and that gives players less to log in for. I miss the 'local' community that 25man guilds brought to players.