If you follow the game-behind-the-videogame-game, perhaps you noticed that IGN's review of Grand Theft Auto IV appeared on Friday, where everyone else's reviews showed up a few days later. This indicates that IGN was likely given the exclusive right to run a review early, and thus earn the traffic that that might gain.
As Variety's blog, The Cut Scene, points out, the idea of exclusive reviews is "ethically troubling." While no one is impugning the objectivity of IGN's review, it does raise the possibility that a news outlet granted a special, first review, has reason to give the game a better score than it might otherwise earn.
With GTA IV, it's less obvious, as it seems everyone is giving the game high marks, but if the game wasn't so great... perhaps you could see where this might lead.
TheCutScene: Exclusive reviews are ethically troubling