Depends how it is set up. Most of the Final Fantasies and other traditional turn based games have incredibly dull gameplay, but they are remembered for their stories. Some other games may have a decent story, but have much more engaging gameplay--a recent example is Grandia 3.

'Video Games' are meant to have interesting gameplay, but RPGs and Adventure games like the Dreamfall series have always been an exception.

More and more games have been breaking from the traditional 'RPG' genre, like the 'action-RPG', and even more games are including 'RPG elements'. The 'ADD generation' of gamers need more than selecting commands from a menu in order to enjoy a game.

So, for an RPG in the traditional sense, Story is most important. If it has lame and uninspired Menu-based battles but a pretty interesting story, I can deal with it. If both the story and gameplay are equally lame, it's a drop in the bin.

On the other hand, if it is actually fun to play--regardless of the story--I would play it.