Ever since World of Warcraft launched, subsequent MMOs usually (EVE aside) go a little something like this: they launch, they do OK, then numbers slide, then they disappear. Not so for Lord of the Rings Online.
Maybe because it's based on Lord of the Rings, maybe because it's actually good, we don't know, but we do know that, according to developers Turbine, the game's user base is on the up and up.
Good for you them! The more viable games (and thus alternatives for players) in this genre the better.