I think the people complaining about how the choices you made were irrelevant with how the game ended isn't too familiar with life in general. I'm not saying that to be a condescending douche, but like life this is game is about choices.
And life is what happens when you make other plans to paraphrase an old saying. How many times have you personally in life set up plans and things in motion so down the road something would happen only to have something come up later and ruin everything you've set up in the past?
Same thing happened here.
So yeah shepherd made all these choices which at the time was the best he/she could do in a crappy situation. Sure in those instances it led to peace, or a resolution for future relations without war between former enemies, etc, BUT when you got to the end of the game you had three choices and you had to make the best choice you could with your limited options.
So I'm not saying there shouldn't have been a happy ending, or whatever, but sometimes life and the choices you're left with don't work out that way.
Sometimes you just get dealt a ****ty hand no matter what you've done, and you have to make the best of a ****ty situation. Shepherd had to worry about saving the entirety of the universe with only three options. The alternative was to do nothing and let everything die.
Sometimes life just sucks like that
I'm guessing they didn't put a final pin in the other characters because they wanted to continue the story via DLC for the future. I'm not saying it's right or wrong, but if they closed the book on the franchise and characters then they close the book on any future DLC/game play. I'm not saying I want to pay for an ending, but if it means I get to continue the adventures of the Mass Effect universe (this is the last 'game' after all) for some time to come via DLC, it's a small price to pay.
I'm not saying the ending was good, or the ending was bad, but sometimes like life things don't end the way we plan on it