Personally I love the ending, It is not cookie cutter happy ending crap a la Uncharted. It makes sense for the Mass Effect universe, the whole point of the reapers saga is that there was a tragedy about to occur. It would be silly if it ends like the war of the world... ohhh look reapers got a cold, they dead now.
Mass Effect at its core its been about the conflict between Organic and Synthetic life, I think the ending gives resolution to the Reapers cycle and puts out there some good questions about this dilemma. Of course internet people is disappointed because there was no Tali-Sheppard kiss on the citadel cut scene at the end.
but you know.. internetz people..
I don't know about everyone else but while I would have preferred this "Tali-Shepard kiss" ending, all I wanted was closure. Not more questions than answers. That's just me though. Can't please everyone but the ending just didn't fit with the fiction. And magic space God kid who died in the beginning of the game throwing these crazy choices at us that have nothing to do with three games worth of decisions does not bring closure.
It's natural for people to seek closure, people want to organize things in neat little piles so they can "get over them" but that's not what real life is like. And while you could argue that ME3 is not the place for arts-y narrative conclusions, I found it kinda brave and interesting.
That said, I got enough closure before the last fight, on Earth, and then with Andersson and Illusive Man. It was enough for me.