Some quick comments, probably think of a hundred more.
Classic wow - less frenetic, quests were hard, leveling was hard and raiding insanely hard- never got near Naxx. So a piece of T3 was like gold, truly epic. Looking back content was a bit bland, but you have to see it for what it was. SM and Schola my favourites.
TBC - Improved questing and instancing . Some areas were great some not so, Attunements were hard in the beginning, Heroic dungeons were hard before badges. Badge gear and nerfing slowly destroyed TBC. But I guess its about money and this brought the crowds!
Loved Kara, still my favourite place remember going in there in blues (there were no welfare epics) and getting horse wiped by first adds, still remember Grom's axe dropping still have it in the Bank.
Wotlk - Epic questing, story lines etc, brilliant part of the game have you ever looked at the detail in Grizzly hills. I really enjoyed leveling my 2nd toon after the crowds had rushed through.
But leveling was a joke probably died 5 times in 10 levels from Dc's more than anything. Instances are a joke and Naxx is a bigger joke. Its ugly, empty and bosses are basic to say the least, there is bad lag it full of bugs and the entire 11 million wow population are there every night.
I though Shat sucked as a city but Dalaran is worse lagging and small - fail on this one
Overall TBC is the one for me, feel I am drifting from the game and don't think Uldar will change much, the masses have spoken with there wallets.