Tbc has like ten zones and trivializes 1-60, makes azeroth a ghost town, flying mounts is the beginning of the end to destroying the real world immersion as you fly over every single obstacle and PvP.
I get really turned off knowing lvl 61 greens are on par or better than raid gear from classic raids. Yuck.
Tbc is the beginning of the end my friend. If they bring tbc servers I will be rerolling on a fresh classic server.