That was... Disappointing at best. What sloppy writing, and sloppy extrapolation, and ultimate laziness in constructing an ending. I haven't seen a set of writers drop the ball this badly in a long time.
Let me preface this with: I love Pyrrhic victories. I was expecting Shepard's death. I was expecting massive sacrifice, and potential loss. I actually liked the beginning of the synthesis ending, and its thematic arc. What I wasn't expecting was a game built entirely on the significance of difficult choices and sacrifice to have only one goddamn ending. And one that doesn't actually make sense in the context of the universe and the "path" I chose in the last moments of Shepard's life.
The final scene that each of the three choices results in - the old man and the child discussing the myth of "the Shepard" and of the possibility that there is life on other worlds - effectively renders every choice you've made over the course of potentially five years playing the games completely meaningless. (Not only that, but the fact that the only choices available to you are all a form of giving in to the vast and unknowable endgame of the species that created the Catalyst, and therefore the Reapers, to begin with.)
That doesn't make narrative sense. It's out of character. There should have been at the very least a renegade trigger to allow you to tell the Catalyst to fuck off, and to take your chances defeating the Reapers instead of letting them, effectively, win, and destroy galactic civilization though saving lives. Even if that choice resulted in defeat, it should have been an option.
And, I have another big, big, big fucking problem with the writing, here, too.
I liked the synthesis ending, until that last cutscene. I appreciated the sacrifice to unite synthetic and organic life to move forward into a totally new form of cycle, a totally new galactic civilization. I appreciated the symbolism. I quite liked it, actually.
But then we still get the ending with the old man and the child that proves that, despite your sacrifice to create a new kind of life and galactic civilization, it doesn't matter. It's the same ending that you get if you destroy synthetic life, or control it. And, by the way, those two endings are supposedly the ones that don't result in a new cycle, but simply trap you in the old one. So, why the shit are the endings the same?
That makes literally zero narrative, extrapolative sense. It is actually impossible. Sloppy, lazy, rushed, bad fucking writing.
And here's a giant plot hole for you, in the synthesis ending resulting in the exact same thing the others do. So, the mass relays are destroyed, yes? Trapping the forces that were around Earth in the Sol system. Temporarily. Do they genuinely expect me to believe that all the technological knowledge of these people was lost by magic? The Protheans once constructed a mass relay of their own; we know that. Why would the gathered foremost minds in the galaxy, scientists and soldiers alike, not be able to make progress toward rebuilding their interstellar travel systems? And, better yet, these are all now synthetic/organic hybrids; they are a new form of life, capable of new things.
Imagine the geth with their newfound individuality, and the quarians, and the salarians all working feverishly to be able to return home - to reverse engineer technology that they've plenty of experience with already.
Again: zero narrative sense that this doesn't happen, and that instead the galactic civilization collapses entirely, and the technology is all lost. I believe it in the case of the other two endings; I don't believe it in the synthesis ending, where it's goddamn impossible for that to happen the same way. Or, should have been if any thought had been applied in the last stages of the writing process.
The logical - and still uncertain, still painful, still all about sacrifice and impossible decisions - ending to the synthesis option would have been a last cutscene showing the different races, trapped on their planets for now, working to reconstruct the mass relays. Physics hasn't changed, guys. The galaxy is now populated by hybrid organisms, that I fucking assume can do as much or more than the original civilization that built the relays, constructed the Catalyst, and laid out the plan for evolution of the galaxy.
It doesn't ruin the games for me, but I'm extremely disappointed at the laziness and bad writing and bad extrapolation. I love unhappy endings, and I was totally down with the synthesis ending as my "good" choice, sad as it sort of was and uncertain as it should have left the future of the galaxy. But losing all of the tech, and the new organic/synthetic hybrids being just as helpless and just as disconnected and just as defeated as the people in the other two endings? That galactic civilization is ultimately destroyed no matter what you do, when the synthesis option exists?
Seriously, if they wanted to do the ultimate Pyrrhic victory thing, the only options should have been the red/blue endings. Using the same ending cutscene for the synthesis option is, frankly, stupid, and shows very little thought. The endings couldn't all be the same, if I accept the context and worldbuilding the rest of the 80+ hours of narrative-building the Mass Effect games do.
(Also, and I repeat, a game that's about making literally thousands of choices over the course of years of storytelling only having one ending? Not on, Bioware, not on.)