The question is not quality. Quality wise the story of Bioware's games are better than average in most cases with a notable exception for NWN 1 OC. The problem is that they tend to follow a formula, a formula that they have used several times, though refined, it has become tiresome.
Bioware needs to break the formula and to do a more innovative story in their games. They need to overall themes and plot structure to be different. They have followed the same basic story structure in NWN 1 OC, kotOR, and Jade Empire which now it looks like they are doing so again with Dragon Age.
They think that this formula writing is what has made their games a success. It isn't.