The question is, how much are you asking of the story?
Are you asking it to be so damn good that it beats World of Warcraft?
Are you asking it to be so good that it advances the entire concept of game storytelling in a new and awesome way?
Or are you just asking that it be a satisfying and important part of the game?
The way it works in Final Fantasy XI, the story bits are just entertaining cinemas that let you get to know major characters in the game world. The payoff is that they're well written, teach you about the game world, have nice cinematography, animations and music backing them up. It's not interesting because it represents how awesome of a roleplaying system it is, and how big of an effect I have on the game world, it's just inherently fun and interesting to watch.
In other words, it can be really nice to have well done story sequences that are polished, and that you enjoy. And it kind of makes sense to use story to differentiate the game, because you kind of choose your game based on the world it's in. I chose Final Fantasy because I like Final Fantasy. People will choose KOTOR because they like Star Wars.