The writing was terrible, it seems like they had an incredible narrative set up for the first one and then they realized that they need to continue it and everyone fell flat on their faces.
But the premise is so good that even that wouldn't be able to kill my interest for the third one if not for that ending.
They also turned the most interesting antagonist of the last 2 generations into a one dimensional cartoon villain. While also introducing a few more one dimensional cartoon villains.
Not sure how they could've fucked up so bad. ZD was my game of the decade, and while it's impossible to repeat the success of that story again, they could at least do a ME2 to their ME1. Instead it's more of a Mass Effect 3…