I just beat it and wow this is the worst overreaction in the history of video games. Oh noes, an ending that doesn't answer every damn question and leaves things to interpretation. The SCOPE of the game was so incomprehensible when talking about galaxies and the universe and such that an ending like this shouldn't be a surprise. Hell, the game had a depressing, end-of-existence tone to it that should have lubed us up for what was to come (the ending). It's funny reading these replies...I only read the first 3 pages but it's way over the top. There was even one guy who said ME2 had a better story, rofl. ME3's story, characters, writing, dialogue, voice-acting... GLORIOUS. Holy fuck, how can someone say ME2 had a better story. Such fucking gross hyperbole, my god. It makes me mad.
And FYI the fact that the 'guardian' or whatever we should call him was the kid doesn't have some deep, underlying meaning. The kid was just one of Shepard's strongest memories so the 'guardian' took shape in his form. The actual kid had nothing to do with anything. Do people really not understand that.