It's been mentioned how the people that need this review advice are the folks who never visit the forums. So how's this for an idea:
Occasionally GOG will do a gem highlight thread, to draw attention to a game that may be overlooked. We could do something similar, but instead of highlighting a game, we have the forum community go in and up/down vote all the reviews on the gamecard page. A sort of "sweeping up" of reviews, to try to clean them out by making sure crappy reviews sink while more thorough reviews rise to the top. We could do one game a week, so we could get them all sorted in only 567 weeks. : / On the plus side though, by having a lot of attention fixed on one game at a time, folks could see a noticeable improvement on the reviews, even if it's only for one game, and this could give greater encouragement to continue fixing others since we'd see something getting done.
Another idea is to alter all those giveaways where people give a game if you vote for something on the wishlist. Instead, have giveaways where people have to go up/down vote reviews for a certain game, to help clean them up.
If the reviews and ratings are being messed up by people who never visit the forums, it's then up to the forum to do what it can to counteract that.
tinyE: I still like the 1 to 5 hard-on system of "Penthouse" but alas I don't get to make these decisions. :P
I like rating hard-ons. That is to say, rating the hard-ons of others. GOG could definitely do with more hard-ons for us (me) to rate.