I'd only support such an endeavor if all reviews had to be submitted with a 500 word minimum review of the game. If you can't wax eloquent about why a game is awesome or why it sucks, then you have no business reviewing a game. If it's just "lol, Gears of War sucks because it's a Microsoft Exclusive" or something lame like that--a rating that isn't real because it's just from someone who owns a different console, it can easily be filtered out because it's kinda hard to fake five hundred some words on a game you don't own.
Or maybe Rotten Tomato that stuff, go with a 'cream of the crop' rating, so that people who are too lazy to rate things can just click "I liked it" or "I didn't like it," and you can take THAT score with a grain of salt.
Oh, and let people change their review scores, because I'm pretty sure many people, at one point or another, have severely regretted letting various GOTYs get GOTY. I've seen quite a few comments about this.
Additionally, block all scoring for, say, two weeks. Hard block for two weeks after release--no one can give a score without having some quality time with the game. Then do a soft block--that is, you can't score a game until clicking "I have played this game," and after two weeks, you're given the ability to post your review and say YES or NO on the "Should you buy?" option (because screw scores: "should you buy" matters more).
That said, I've always enjoyed how Flickchart works. Instead of letting you stack the deck ('ooh, it's X, BEST SCORE EVER!'), it presents two random movies. Assuming you've seen both, you pick which one wins out, or click "I haven't seen this" until you've got two movies you have seen. It presents some really interesting conclusions. Still not reliable, since The Dark Knight was THE BEST MOVIE EVER according to the last time I checked Flickchart.
But still.
It'd be interesting for games.