I'm not sure that I understand the complaints of people who are upset about the game not being in their favorite setting, and how it will "shoot themselves in the foot" by not putting it in The Realms / Planescape / Greyhawk / Etc.
First of all, it's going to be D&D mechanics no matter where you put it.
Second, no Massive Multiplayer online experience, due to the different clientele it attracts, will be the same as an actual roleplaying game. As someone said, it's a MUD with 3D pictures. The people who play 20 hours a day are going to outstrip the rest of us, and are always going to look for ways to "win", or "collect goodies," or (in some cases) outright cheat. It's those who will spoil the fun of both those who want to role-assume, and those who want to just knock off a few hours in a day hooking up with real people and fighting dragons.
Third, I'll probably never get hooked on it, or even try it, because there are too many things to do, like run my pen-and-paper games. I am so used to the P&P experience, that even if I had to use it as my sole gaming "fix", I'd drop it out of disappintment. I'm waiting to see if the game environment itself is truly different, and go from there. No Player vs. Player for me, thank you.