I played wow since release. Quit about a year ago. I played a lot.
I had a huge amount of fun exploring the world in vanilla (1-60), and almost as much fun leveling different classes finding out what I liked.
I loved instancing, most of all with my friends. I liked gathering gear and watching my toon get stronger...but after a while you've seen all the classes, done all the instances, got to max level, maxed your professions...and whats left? 2 things.
PvP: Which I will never touch because I like a more or less level playing field. Winning in wow is about having better gear (mostly). I like to win because I'm best, not because I have spent 10000 hours grinding the latest pvp gear.
Raiding: Which amounts to the same as doing the same instance over and over again, only its harder and more time consuming.
The story is weak and terribly presented compared to almost any other gametype, and it is well hidden between mountains of crappy "go here kill 20 wolves" type of quests. The gameplay is the definition of repetitive and in the end, its not really a game its just another job THAT YOU PAY FOR.
It is completely not worth looking into, you can have as much fun in other games that dont require a monthly fee and will not eat your social life.
There is ONE thing I miss about wow, and thats not wow its the people. I had a load of fun with my guildies and I miss the socializing, but on the other hand its nice to have the week off instead of having at least 2 nights planned for raiding EVERY WEEK.