Russ has an excellent write-up on the World of Warcraft experience.
I did indeed go buy it on Saturday after badminton, and I gotta say .... wow. It's with good reason it's also known as warcrack. I think I played for maybe 20 hours over the weekend, and I never play games for that long. Actually, I rarely play games - Half-Life 2 was the first I'd bought in about four years, and that took me about two months to get round to completing.
I've never been a fan of D&D but don't let that moniker fool you. This game is action, adventure, first-person beat 'em up, whatever - it crosses several genres and looks amazing. And as Russ mentions, the place is huge. HUGE. John has also been playing, and it took me an afternoon to cross from my part of the world to his (including taking an underground tram). And that represents a distance of less than one eighth of the map. Ouch.
The thing that gets me most is the interaction with other players. See someone getting beaten up? Help 'em out. Need more people in order to defeat the bad guys? Form a group and act in unison. Get helped out whilst being beaten? Say thanks. Suddenly, you're playing and chatting and joking with people who could be on the other side of Europe. Incredible. Of course, the fact that it's real people in there does lead to some quirky issues - like late on Saturday night (well, Sunday morning) half the characters in the game were stood around motionless. I guess their owners had fallen asleep.
Another nice thing: you can create lots of different characters and play as whichever one you want. I have two characters on the go at the moment (one of which is playing in a team with John), and it's quite good fun to see how your style has to change based on your character's type. You can't stealthily creep around when you're an 8 foot tall bull ;-)