I would first like to point out that there will be MASSIVE SPOILERS in what comes to follow. I will be detailing my thoughts and experience with this series. I want to feel out what made this game so good, to help explain why the ending fails so horribly for me.
For me, Bioware created this amazing, compelling, detailed, and expansive universe in Mass Effect. One that, in my opinion, rivals any created to date. The attention to detail was frankly stunning. Even planet had its nuances described in its lore, if you so chose to read them. While I did not read them all, I appreciate the time and care that must have took. They put care into making subtle references to decisions you made in the previous games, and sometimes not so subtle references. While never perfect, it blended well and really immersed me into the universe.
The games themselves challenged you to make decisions. You could certainly ignore them, arbitrarily chose them, or carefully pick them and experiences the consequences great and small. There were times you had to chose the life or death fate of a squad mate and deal with the remorse. There were times when you had to fight morally and ethically about the future and direction of an entire race. You had to wrestle with centuries old conflicts and help work out a resolution, good or bad, or rather paragon or renegade. Through it all, though, my Shepard was stalwart and uncompromising. She (femshep for the win) was a legend, not because she chose to be, but because that was what was needed. She fought knowing it needed to be done, that she could not give up, not just for the sake of herself, but for the sake of everyone. She would hold the line.
And then we get to the ending of Mass Effect 3. I do not even know where to start. Throughout the game, it had been building to this final moment. The moment to stop the Reapers from destroying all space faring life in the galaxy, centering, for the moment, on Earth. Shepard had gathered all the races in the galaxy together for this one push to retake Earth, and reach the Citadel to complete this final weapon. The galaxy is on the line. Everyone knows this. Everyone is prepared for the worst. Shepard’s core team has been with her through thick and thin. And in those final moments, the most uncharacteristic (for this series) things happen.