You've got it backwards. It's "no amount of story can make up for horrible gameplay" . For me, above average gameplay can easily outweigh a poor story, because I play games because I think it is fun to play them. Some games have great stories, and that's a cool bonus, but it is very rarely what makes me decide whether to keep playing it or put it away forever.

FF13-2 had the worst story I have ever seen in any game in my entire life, and I still enjoyed playing that game, once I was done with the story part.

I think you missed the mark with bringing up Halo, though, but maybe not. Can you tell me exactly what makes a game a RPG, and what makes it not an RPG? When does an action RPG stop being an RPG and start being an action adventure? Is Mass Effect 2 a RPG? Is Zelda a RPG? Is GTA San Andreas an action RPG?