writes "In a study presented at the Human-Computer Interaction conference in Cambridge, England, British researchers Beale and Bond found that plot and graphics are not critical to the success of video games; price and the inclusion of social aspects (e.g. multiplayer or chat) were found to be more important."
An unfinished version of the paper
(PDF) is available from the researchers' web site. They said, "One of the most unexpected findings was that gameplay was not featured as one of the most important categories to fulfill," though they acknowledge that variety and cohesion were measured separately from gameplay, which past studies have not done.