 The games in the series have been praised as being among the best first @-@ person shooters on a video game console , and are considered the Xbox 's " killer app " . This led to the term " Halo killer " being used to describe console games that aspire , or are considered , to be better than Halo . Fueled by the success of Halo : Combat Evolved , and by immense marketing campaigns from publisher Microsoft , its sequels went on to record @-@ breaking sales . The games have sold over 65 million copies worldwide , with the games alone grossing almost $ 3 @.@ 4 billion . 
