Bells and whistles and plot charts are fine, but let's not lose sight of what this really is: a single and highly-controlled channel through which game information is relayed to the user. Should anyone come to rely on something like Game Advisor, they will know only what they are told. To be fair, there'll be a host of options for them to choose from, I have no doubt of that (as anyone with the latest, greatest game rig usually does), but they will be artificially limited. Microsoft would have no incentive whatsoever to inform you of anything that does not benefit them directly.
I'm not raging against MS when I say this; I would honestly make the same criticism of any company who would contemplate this, whether they're iD, Valve, GameSpy, Blizzard, NCSoft, IGN, whoever.
Edit: fixed typos and formatting
This comment was edited on Jun 29, 22:48.