I've played right through Mass Effect 3 so I can say that the ending was as epic and mysterious and final as I expected. I can understand why people are upset about it, but I think they are overreacting and aren't properly understanding what happens at the end... At least, that's my opinion.
Besides, its Bioware's story. They can end it as they want, whether we like it or not.
Edit: Perhaps I've been conditioned to obscure endings due to having watched Evangelion: Death and Rebirth. Although that still takes the cake in the weirdness stakes, lol.