If they had just not bothered trying to give the Reapers some higher motive and purpose and just kept their motivations a relative mystery and kept the Crucible a vague deus ex machina that kills them and then put all their focus on ending scenes that varied based on our choices from through the series and final game, even using the whole weird Galactic Readiness rating to greater effect, then most people would have been very happy with the ending.
