Have to agree about TBC. It was the best expansion. There was loads to do, it still had the challenge element and group element incorporated yet it stepped away a bit from the insane grind that vanilla required.
Content was puggable if you were a decent player and generally the old communities were intact. Hell on my server it was so friendly myself and the 2 other boomkins from the other top ally guilds (guilds 1, 3 and 4 on the sever, horde guild had spot 2 /shakesfist) used to organise "learner runs" to help out new players and help guide them through Kara, Gruul, Maggy. We were only dps so the new players had to take on the key roles and it was good for them and great laugh for us. At one time we got all the best druids the top 3 guilds (who everyone knew by name on the server pretty much) and we 10 man druid ran Kara

extremely difficult without any CC (roots didnt work indoors back in them days) but we somehow got through, I will try and find the screenie off 10 triumphant druids standing over Melkazhaar

(or however you spelt the last boss in Kara name) We also had our sunday night "Dance off in Darnassus" which used to get crowds watching of between 20-100 players 3 boomkins having a break dance, cheesy but good for the lol's

We were Bjorni, Starfall (I think) and Boomchicken. Great times
It started the slide toward the end of TBC with pre-quests and raid pre-requisites removed (like killing Vashj and Kael before moving onto BT) then they nerfed the toss out of the raids but still great fun!
Kara and BT were the raids I still love and have nostalgia runs in, sooooo atmospheric! Used to love how difficult the last Hellfire dungeon was on heroic as well

even full BT geared if you missed a step you were toast
But yeah, despite the old days that I miss it still entertains me and is enough to keep me playing if not loving like I used too.