I had the best WoW Fun ever in Cata (started in 3.2, before that i played barely some privatservers/test account for maybe ~ 20h).
Cata was the best Addon for me, cause i had so much fun with friends, playing 24/7 RBG with my Guild and just like the Gameplay... But Cata got worse after everypatch (bad changes to Arms warrior, my main) and 4.3 was the Kill for the Addon. Raid Trash, Arms Warrior super Trash, RBGs just Hackers and Dotcleaves, where everyone had the Firelands Legendary + Rogue Legendary and broken PvE Stuff...
And cause the classic versions use the balancepatch from the latest patch cata classc would suck ass.