I believe WoW is having a free trial atm, why not give it a spin. Worse that could happen is you like it
I myself have played many MMO's, not WoW or Guild Wars but I had friends that did. I've played Asheron's Call, Asheron's Call 2, Star Wars Galaxy, Dungeons & Dragons Online, and my favorite addiction Final Fantasy XI Online. I would say most MMORPG's are tough if you're just a casual gamer. You really end up sinking alot of time and it's not like most games where you can "beat the game" by any uncertain terms. Basically an endless game.