EQ took my MMO cherry at the tender age of 15. RIP High School initiative. Vanilla WoW had the same effect. No other games have come close to those (approx 2yrs each) experiences.
I think there is something about the unknown and danger that vanilla games have. Then you level up, you have been all over the world a dozen times, you become goal focused. I remember the most fun I could have would be with a friend and we would run around leveling, exploring, trying to go into zones that would kill us. Something magical about that newbie experience.
I miss this too, the new zone scaling/instancing stuff is cool from a tech standpoint, but nothing feels dangerous anymore that's for sure.
I hope to see a roguelike multiplayer RPGs where things can be random, surprising, broken, confusing, (hopefully not to frustrating) created a deeper sense of adventure.