Nice article by James W. Hall in the Wall Street Journal.
Good example. I thought the first Larsson was pretty poor except for the character of the girl and the lurid descriptions of rape. Those two aspects got it attention, plus the fact that it was a Scandinavian writer when Henning Mankell had just risen to bestseller status. Then the publicity machine started in and created a mega-seller. The fact that the author had died also helped.