I never was a huge MMO fan. I played a few in the past like Dungeon and Dragons Online, LaTale, and recently Tera. With the exception of LaTale I kept getting annoyed with the floaty controls. I don't think I payed attention to the plot in any of the games.
Right now I'm putting my money on Elder Scrolls Online. It's turning out to look like a revolution to the traditional MMO. They are extremely dedicated to the story and lore and the gameplay mechanics are going to be for the most part an exact replica of the
Elder Scrolls games and while embracing the holy trinity they are also trying to break the mold by having very adaptive builds in which it won't be required.