(Related post: Raiding does not mean Skilled)
World of Warcraft, and every game like it, is really two different games. I first read this thought at Penny Arcade (can’t find where because their search function is weak). Basically, you have the levelling game where you start at L1 and then play until max level (currently L70), and then the game that happens after the levelling game, which is filled with group activities of all sorts as you improve your max level character.