I'd say the vast minority (something like 10-15%) of people who play games even read game reviews. And less than that percentage read those reviews to have them influence their gaming purchase. Factor in that Final Fantasy has always been a game that has a pretty solid fanbase and most people were already hyped for the game, the only people who would really be swayed by 'reviews' were people who would have most likely been leaning towards not getting the game already, and the review was just an excuse not to get the game.
Most likely, they would have put off getting the game in the first place until a 'friend' or 'another game' gave them an excuse not to get it. In short, I don't think reviews are a mjaor factor to the sales of FFXIII.
Six upcoming games you should look into:
