Understanding my thoughts on ME3's ending requires a bit of context of the game to me, and no doubt others. Mass Effect was never a perfect work, but it sure had style, and it was refreshing to see new IPs go over well. ME3 moved things a bit forward though. Video game story telling has always been very limited, mostly due to a lack of effort. Assuming they even try to have a story beyond a framing device, it's almost always self contained. There's no buildup between Zelda or GTA games from the last in terms of story as it always restarts. Of the ones that try, you either see them drop off the face of the earth like Half Life, or drive themselves into the ground trying to keep it going like Resident Evil. Unless it's planned like .hack, serialized stories in video games would always disappoint in one way or another (with MGS4 being the one exception I can think of).
So ME3 starts getting hyped up, and it looks like they're going to tell the finale of the story they've been telling. It comes and it's cheesy, a bit flawed, but no more than any other sci-fi story, and it was doing a decent job of playing to all the fanservice we wanted. It was grand, it was epic, and it fumbled at the one yard line. Suddenly the conflict of 3 games, 4 novels, and a dozen comics, that had been summed up as "can we beat the reapers" shifted to ""SHOULD we beat the reapers." Now they had a purpose to the universe. A flawed, but well intended one, and in 10 minutes we're expected to dissect their motives, the actions of the galaxy and decide the fate of the universe. It was like if Return of the Jedi had Luke ponder joining the Empire, or Frodo had been sane and still thought about keeping the ring. It might have gone over better, but most of us could see the flaws in the reaper logic, especially if you united the Quarians and Geth earlier in the game. Most of us wanted to shout down how their principle premise was proven wrong, and how there's more to a species than their genetic makeup, but common sense was lost in 3 forced choices. A cheap "Marooned" finale for the rest of the cast added salt to the wound.
I wasn't angry, just disappointed. All they really had to do was have a big battle, and they thought they could be deep and thought provoking. Anger generated in the weeks to follow as the fight become rooted not in ME3 but idealistic views on content creation, which cemented into bitterness over time as if I'm unhappy and make my voice known, I'm an entitled fanboy for daring to tell a creator what to do, but slap the word feminist on something and you can rip and created content apart without concern for the creator's whims and desires.