If I had to choose between a game with mediocre gameplay but an amazing story or a game with fun gameplay and no story, I wouldn't hesitate to choose the former. But, ideally, gameplay should both be fun AND help to make the narrative deeper. Think about how awkward Wander from Shadow of the Colossus is with his sword for an example. It's because he stole that sword so he could use it to bring his girlfriend back to life, so he just doesn't know how to use it properly; a perfect example of gameplay helping to tell the story. Plus, sometimes good or unique gameplay just isn't enough to make a game interesting. After all, would Portal have been nearly as fun without GLaDOS? I think not. GLaDOS and the subtle narrative she helped provide accomplished something that no amount of clever puzzles would have been able to on their own; making one of the best games ever. Without a story, Portal would have been an interesting but otherwise kind of boring experience with hardly any replay value. So, story is king in my eyes.