World of WarCraft is so loved and played because of the legends that previous WarCraft game has set up.
I remember playing on Battle.net and some people constantly chatting about WarCraft becoming a RPG or a Action type of game.
People and friends in our circle who also played WarCraft talked about WarCraft becoming that sort of game.
On parts, WoW has such a long history portrayed by their series of WarCraft games and Campaign Maps, the desire to relive and create your own legend through a race you'd like to be, becoming a part of either side's history; Alliance or Horde.
The RPers (Role Players), as they are commonly referred to, like to indulge themselves in a environment where they can interact with other players in a community. It's all part of having fun (I like to RP sometimes
).
On the gameplay side, WoW (from my view), was quite the most easiest and fun MMO I've ever played.
The battle system is as real as it could get, leaving other players frustrated, wanting revenge or bloodthirsty and out for more (I love to PVP.)
The level/experience system in WoW is actually one of the fastest systems I've ever been on. In a total gameplay time, I got to level 60 in matter or 13 days.
WoW also has other intriguing ideas such as the
Quest system (I know other MMOs also have quests, but WoW has a whole range of different quests you can play into),
Raid system (It used to be annoying because most of it consisted of more than 20 people raiding at the same time, resulting in slow, time-consuming progress of the dungeons),
Faction system,
Honor Ranking System (the new system is reasonable, whence the old system required the player to play 24/7 with PVP groups), and... etc, because I have to get my breakfast.
IMO; I think WoW is so popular because of the so many possibilities it gives you through their diversity of Race, just the right amount of Classes, the legends you could create through RP/PVP, and just for sheer fun of teamwork through Raids.
I liked it because I simply loved to fight, teamwork, have a little gaming fun with friends, and mostly due to my love for WarCraft.
[ This started to turn to colloquial in the end... probably due to my hunger. SEE?! ]