Alright ima pour my brains onto this post.
To me, MMO's have 3 general sections. Generic, generic with flare, and Non-Generic. WOW is the best game in the generic section, and then below it, every other generic mmo. Then, games like flyff are generic, but they have some flare to make it more fun (flying). But flyff actually has combat in the air, and a lot of other flying related things that it might even be considered non-generic. Other non-generic mmo's are the first person ones, like Darkfall.