1) Add a real prologue section so that there's real drama when the sibling dies (also we get to choose which sibling to save for extra drama)
2) Have the sibling as more than a pawn for cheap drama
3) Possibility of saving Leandra (then she dies in the Chantry explosion, adding a personal punch to the situation)
4) No underwear during romance love scenes...it's just stupid
5) Have Anders blow up the Chantry in a less confusing and out-of-nowhere manner
6) The Sides you can choose during Last Straw.
Being forced to choose Mages and Templars when the game's failed to make either side appear anything more than a dark/dark paradigm is just weak. The additional fact that the endings to which ever side you choose are identical pretty much negates any real impact that the mission had.
Mages: fight templars, possibly fight Carver, Orsino goes nuts, Hawke kills him, mages lose, Meredith goes nuts, Meredith dies, templars leave Hawke alone.
Templars: fight mages, possibly fight Bethany, Orsino goes nuts, Hawke kills him, mages lose, Meredith goes nuts, Meredith dies, templars leave Hawke alone.
Might as well through in a third option to tell Orsino and Meredith to f@#% off. Hawke has no reason to feel pressured into choosing a side, how about making his own side with flapjack and hookers? Okay scratch the flapjack and hookers. How about having Hawke step up as de facto leader of Kirkwall and tell Meredith to back down and for Orsino to come clean?
Kirkwall: Fight mages and templars, persuade Cullen and elements of both factions (including your sibling) to join you, Orsino goes nuts and Hawke kills him, Meredith goes nuts and dies, Cullen calls off annulment, Hail to Viscount(ess) Hawke.
Out these six, the last one would be the one that I'd really want.