Raph covers a detailed study of how to improve game marketing, citing many of the quotes from the pdf like "Positive word of mouth is a key purchase requirement for all games," and "Graphics, price, gameplay, and features were the top factors contributing to a customer purchase decision whereas buyers are barely concerned with the publisher or developer." His post is worth a look, as is the original research (pdf).
One of the things he points out, which we've been sort-of discussing here for a while, is the potential of social networks for spreading information about products. Already, many purchasers do rely upon formal or informal social networks for their game-related information (via magazine/online reviews or friends and family), but, as Raph suggests,
It's actually rather surprising that so few attempts at social network marketing have been done in the games space, outside of occasional one-shot "invite a friend" promotions.
I'd argue that at the minute most of the advertising and marketing is being directed at a social network - one made up of gamers. The problem is that it's not going beyond that to the rest of the population.