The Charnel Expanse wrote...
It's pretty clear that in crafting the ending, the two men ostensibly responsible for it completely lost track of what has been the established central theme of the Mass Effect trilogy - the struggle of one wo/man to unite a galaxy against an existential threat and the difficult choices s/he is forced to make in the process. It's a simple theme and one that should not have been difficult to stick with. Instead, when it came time to conclude the series, they took what had been an existing but ultimately ancillary theme in the game universe - the conflict between man and machine [or organics and synthetics, as it were] and decided to wedge that in as the main focus of the series at the very last moment, thus completely upsetting the narrative flow of all three games.
Now, to be fair, organics versus synthetics WAS a present conflict and not to an insignificant degree. Listening to Saren talk during the first game, you'd think that was the focus of the story from his perspective. But in the second game, it was relegated to a very minor plot element; magnified slightly in the third [specifically during the Rannoch arc] but it was never the main focus of the Mass Effect series, and that should've been abundantly clear to two men who were there for the entire creative process. Saren was never the protagonist of Mass Effect, and for the writers to adopt his warped view of the universe is just baffling.
Why they lost sight of things, I could only speculate. But this thematic disconnect is why any attempt to salvage the existing ending will almost surely fall short of satisfying any serious fans. The Catalyst is not completely irredeemable as an exposition fairy character, but damn close to it, because he represents such a disconnect from what the story is actually about, and in order to fit him into the narrative his entire character would have to be rewritten meticulously, to reflect Shepard's view of the universe. Very difficult to do, given how little precedent there is for his appearance in the first place.
No doubt, and there are more than a few problems with this.
1. We were already given an opportunity to resolve the organic-synthetic conundrum with the Quarian and the Geth. For most of us, this had literally been resolved to the happy satisfaction of both groups. But the ending flat out throws that wonderful segment away - why on earth would they do that?
2. The central focus always was, "Stop the Reapers, Stop the cycle". Never was the focus with a supreme being who had trouble making decisions when their toys stopped playing well together. This was both a radical shift in focus with no warning, and worse, was an absurd turn of events.
3. The change in narrative changed Shep from the savior of the Galaxy (or loser, assuming the decisions and actions mattered), to a minor character helping a supreme being figure out the next step for screwing with the playthings in his galaxy. Talk about completely uninteresting gameplay. I mean who looked at that and said, "Yeah, they're gonna love this idea!"
4. As a defense of the ending, we're continually getting a stream statements saying in effect, "The ending is meant to be interpreted" and "We wanted to generate discussions!" (Check on that one!). But most successful narratives that do this (2001 Space odyssey and the Matrix, for instance), telegraph this action from a mile away. They don't spring it at the last second when the entire 3 game series, the model was one where "the story unfolds in the moment, usually combined with life or death action." They simply had not set up a wildly interpretive ending - that approach was doomed to fail.