I have never tried WOW. My previous forays into mmo gaming were the DAOC and Warhammer Online, both pvp-centric and arguably hard-core, particularly the first. I am loving this game so far.
My greatest complaint is that there is no difference in terms of classes btw Empire and Reps which makes the game blander but does cut down on the whinefest. Another issue I see is that as yet I have not observed a tangible reward from pvp a la realm abilities. But in terms of progression it has been so enjoyable that the above mentioned stuff doesn't bother. Of course, after I have experienced the story lines of enough classes and only want to pvp (i hate grinding pve) I might lose interest in this game but with any luck they will expand on that aspect of the game.
I do have a question, how hardcore is WoW, in truth? Because compared to the games I played, it seems not at all. And strangely enough, it suceeded.