--SPOILER DISCLAIMER-- This blog talks about the ending of Mass Effect 3, probably in great detail. --SPOILER DISCLAIMER--
First, let me say that I love Mass Effect. I have loved it since the first game, and I love the final chapter as much as the first and second. I thought the ending I got first was bad, but mostly it was because I destroyed all synthetics, and EDI and the Geth certainly didn't deserve that! However, after my second time through, I was perfectly content with the 'Synthesis' ending, and I felt I had been suitably rewarded for my efforts.
That said, I've heard murmurs of discontent about the endings of ME3. My only disappointment is that the continuity of the story, if and when it occurs, would be completely divorced from Commander Shepard.
One can't even say "Oh, it will be Shepard's descendants that carry the torch". Now, one might say "Hey, when I was Shepard I made it with Liara and/or I was a dude, so my romantic interest could possibly be pregnant!". Keep in mind that the story doesn't require that Shepard be romantically involved with anyone.
Because of this conclusion, I have come to believe that the main reason some people feel cheated is simply because Shepard probably doesn't survive. And yes, we do know that for sure, because we are told that explicitly, so no one go throwing out 'BUT SHEPARD MAY HAVE SURVIVEDED!!!'. Mostly everyone wanted for Shepard to live happily ever after with whomever they chose to share life with and that dream got crushed.
However, I'm not denying that there are many, many other reasons that one could be unsatisfied by the ending. Out of curiosity, does anyone have any comments to share on why they were dissatisfied with how things turned out? Or, does anyone wish to defend the writers' choice of ending?