I haven't played very many MMO's. Uhh...Only like 12.
But it doesn't seem like that many. I'm just curious, which is the worst you ever played? For me, it was FLYFF--In the early levels, which is all I really took the time for, there was really nothing to do but grind. You go to a hill, kill 5 of something and collect 5 something, and then go to the next hill and repeat.
A few hours of that, and I was done.
On the other hand, every MMO gets put down by somebody. I spend a lot of time talking about what makes MMO's great and what would make them better...I wonder what we would learn from identifying the lowest of the low.