If you had to describe the MMO field in one word - without using the words "virtual" or "massive" or "Warcraft" - you could do worse than picking "fickle". It's all but a law of nature that for every game that manages to get big-time exposure, there's another whose very name provokes boredom at best and vitriol at worst. For every Aion, there's a Tabula Rasa... or, if you want to be more ironic, for every Asheron's Call there's an Asheron's Call 2.
But no matter those obstacles, someone will love those games. There is always a fanbase, always people who play the game, always people sad when and if it dies. Maybe it's some quirky system that the game introduced that was interesting enough to overlook the game's other flaws, maybe it's a surfeit of flavor and roleplaying options, maybe it's even just the fact that the game is so badly designed the player gets a strange, Mystery Science Theater 3000 thrill out of the train wreck.
Whatever the reason, we've all got our pet games, whether we think they're underappreciated gems or bad games we love anyway. What's your favorite MMO that no one else seems to like?