Here is an interesting article about how influential are becoming game reviews, up to the point some publishers tie bonuses to metacritic/game rankings score directly. I knew reviews were quite important, but not so much, having some kind of control over those scores could be more important than making a good game actually.
There is another fact they mention, Take Two's stock jumped 20% after Bioshock got a high composite rating on MetaCritic. Scores are important, definitively.
QuoteAbout 18 months ago, Activision also conducted a study of 789 games made for Sony Corp.'s PlayStation 2 console and found a strong correlation between some high game scores and strong sales. Activision Chief Executive Robert Kotick says the link was especially notable for games that score above 80% on Game Rankings, which grades games on a 1-to-100 percentage basis, with 100% being a perfect score. For every five percentage points above 80%, Activision found sales of a game roughly doubled. Activision believes game scores, among other factors, can actually influence sales, not just reflect their quality.