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..