Purely my own opinion here, but BC wasn't epic at damned all unless you were in an active raiding guild. The story was all over the place, and very non-cohesive, and save for Nagrand, the world was piss ugly as hell. WOTLK was epic. It had a bad guy. You saw that bad guy doing bad guy things. All through your experience in the Bad Guy's Land. You KNEW shit was going to go down, and that shit NEEDED to go down. WC3 led up to this. Finishing the fight and all that neat stuff!
Cata was far more lackluster in that department, but it was still better than BC by virtue of being a little cohesive with the story.
MoP is the only one that is anything close to what WOTLK brought to the table.