While I will agree that GTA IV does indeed do a good job of showing consequences of your actions of the main story (i.e. greed/revenge ruining the one good thing you had in America - Roman, humility/forgiveness costing you a certain future with Kate) and with side stories (i.e. saving Clarence after hearing him beg for his life in the
Holland Nights mission for Francis, only to have him attack me in a
random person/
stranger mission after that), I'd hesitate to say it's beaten Mass Effect just yet - for the simple fact that the actions in that game will lead into Mass Effect 2 and beyond, we just haven't seen the consequences yet and it definitely will affect thousands/millions of people and other species. Basically, the scope of GTA IV's decision/consequence system is limited compared to that of Mass Effect. All that, and, Mass Effect came first - so it's the first game to really tack on some weight to decisions
.