I know people say TBC was the best expansion EVER, but nostalgia aside...
What could you do in TBC? Other else than Heroics/Raid/PvP?
And this is coming from someone who started playing in 2004.
In MoP you have endless stuff to do.
On top of the Heroics/Raids/PvP, there is:
Treasure hunting, archeology titles
Pet battles (Which in itself is almost a game),
Achievement hunting (Achievements weren't out until late TBC)
World PvP is back
And I'm probably missing some.
Even though I had fun farming UBRS daily for 3+ months to get my Tier 0.5 Valor chest, I can say that I would had had a blast if MoP content was in there.