OP, it never really was about some super silly happy ending though in effect with the cutscenes and slide shows now the attempt is to show happy endings of the super silly variety. The term is even used to insult those who are always challenged to fully express just what they did want.
For many it was a happier, more satisfying experience. Victory through our own true means along with the survival of Shepard and characters that were important to each fan. But as a possibility, something that was achievable and clearly shown. And not even as the only possibility.
One of the most overriding concerns was basically that is just make sense. That the themes created within 3 games extend to the endings and that major stories have relevance at the end. It also was important that the character that each player "created" using the dialogue and actions Bioware allowed us to choose from, exist at the end. In my game, she did not. That Shepard is not the one I played-and that's possibly very likely where they got the idea of the clone for Citadel DLC. Bioware created options for me to choose from in my game and those options created a specific Shepard for whom the endings were a pile of mush and crapola. So, my Shepard has no conclusion. The endings do not fit the game I played. I might extend that belief to say that I don't understand how anyone can think they fit anyone's game because of the many egregious flaws within the whole post-conduit content, but that would be substituting my opinion for theirs. It's bad enough that they do that to me.
The endings I wanted would have contained variations based upon all that you and I did and were allowed to do in the games. They would never though have disbanded the idea that the destruction of the reapers was paramount and THE goal-it was all along and no one in the game who was in their right mind, ever considered any other alternative to have value. The endings would have (in my perfect game) fully realized the idea that working together (unity) could achieve the impossible and that our differences (diversity) are what make us strong, and allow us to grow and to reach for and achieve better things. Within such endings there would be the sad full on loss type ending, the bittersweet and sacrificial, and the full on win and survival based not on some final contrived choice but as an outcome of perhaps who Shepard was, what Shepard did, and how Shepard did those things. Not a choice but a consequence and goal oriented. Not some final choice given by god only knows who in order to serve the purpose of the most idiotic grouping of synthetics and organics that have ever existed (the kid "AI", Leviathan, and the reapers). It's the most inane thing to have a game about galactic survival with decisions made along the way that were for one purpose instead and at the last few moments be about solving the problem of a "gang of idiots" using some method created by some unknown person or persons (the choices and the crucible plans).
My perfect endings would also have shown real consequences of what has just occurred-not some slides that say "lookie, everyone be smiling-the galaxy is A-OK." The galaxy has been through a meat grinder and so when people say it's the journey and not the destination that matters, well no, it's the journey and the destination that matter-they are intertwined and the destination should reflect in part the journey that has gotten one to that destination. The galaxy needs a hero even more in reclaiming what was lost-but it can never reclaim all that was lost. Rebuilding and renewing, reaffirming life and all will take even more courage. The journey has been crappy and trillions have died from different cycles to get to this point-the point past the reaper reality.
I for one wanted the chance to get to a happier ending, one with consequences, real logic, the ability to play the game through to the end, and especially the certainty of real endings, no matter the "choice". I'd have preferred it all be rational as well. I got none of what I wanted. Glad for those who did.
One last note was that one thing BW said was in relation to all the wishes that Shepard might live and have a reunion with friends (often expressed as just one simple scene that shows everyone knows the others survived). BW said they couldn't do that because everyone would want something different and they couldn't customize such a thing for everyone. This makes no sense. How is it that BW could never make post-ending reunion content because people would want different things, but now they were able to create pre-ending reunion content.
And this issue might never have exploded in the way it did had BW not been the one to create the hype and buzz about what the endings would be. Prior to release it was like they could not stop talking about what the ending would be like. Now, you may fault other devs for the fact they hype their games too, but in fact, BW created this fiasco. Never should have opened the door and discussed how it would all end. No doubt fans would still have complained the ending fails-I could never see this as a rational great cathartic way to end this series, but at least they never would have been hung by their own words.
So, OP, sure I wanted happier, but not bunnies and rainbows-I wanted something more real and pertinent to the stories I'd taken part of. ME3's endings don't fit the game I played and you don't even play the ending at all. It's like one big cutscene interrupted by some button presses. Wee, fun. No, I didn't want a boss fight either, but a boss conversation? How about a true confrontation at least? This kid has been sending monsters to suck the life out of people-so by all means let's sit down and have tea together. STUPID.