Really? For me, TBC was actually a pretty hardcore expansion. They still had attunements, which meant you had to complete the prior dungeon before advancing. It had Karazhan which was just difficult enough, and an amazing launchpad into the higher game content, and they hadn't gotten lazy by recycling endgame content into 10 and 25-man raids, and regular and heroic mode. Only 5-man dungeons which was fine.
Other things I liked about TBC (and prior)
- You had to actually form your own parties, which was part of the social aspect of the game (MMO)
- You had to actually see the content, which gave the dungeons context before just zoning in and facerolling through them (RPG)
- Like I mentioned before and can't stress this enough, there was linear progression which gave players a sense of ongoing accomplishment, from 5-man Ramparts to 25-man Sunwell.
- You actually had to app to progression guilds to see the endgame content, which made it that much more special when you and your teammates got to see new content for the first time.
Blizzard tells me that I am living in the past. On the forums they like to call it "nostalgia syndrome" or "rose-colored glasses" - but that doesn't pass the smell test. The fact is, the changes made after TBC completely watered down the progression aspect of PVE and removed a lot of the social obligations, which affected the gameplay considerably.
The only change made that I love since TBC has been rated battlegrounds.