Well, I think World of Warcraft has won this distinction. If you have never played a MMORPG before, then play this one. If you have played them all, then get this one. If you can that is. Numerous cities have completely sold out it appears. I know in my hometown. I went to get the strategu guide, and not only was that sold out, but the game was too. Not one store, but Media Play, Game Stop, Comp USA and Circuit City. This is no one horse town, but a nice sized city in Colorado. Why do I like it?
One of the main reasons I love this game is it does not force you to group with others. It appears that most classes are suitable for Solo Play. So no more getting stuck with some group of 10 year old yahoo's or waiting for hours to get a group. Just go out on your own. So far in 4 weeks of playing I have only grouped a couple of times. I have created Hunter, Mage, Warlock, Rogue, Paladin and Druid. They all seem to be pretty easy to solo at least to the 16th level.
Second reason I love the game. The questing system just feels right. Now quests seem to make sense. It makes the lower level so much fun. Now instead of just aimlessly killing squirels and rats. You are pulled into the world through the quests. You have the quest log at your fingertips. It gives you plenty of info to find where to go and what to do. You can abando quests when you want. You can keep many going. It is not uncommon to get close to a level just in questing what is available in your area. You will still be killing 12 kobolds, but now you are killign them for a reason. You get the experience for killing, then the experience for the quest and some nice reward. There are so many quests, especially at the lower levels that you never have a problem finding one.