sentences:  The series has also been criticized for its release model in contrast to the "Rock Band" series, causing some players to hold contempt towards Activision.Harmonix considered the "Rock Band" series as a "music platform", and supported it with downloadable content and the ability to import songs from its games and expansions into most other games of the series.Critics argued that "Guitar Hero" should have been doing the same, either through releasing expansions that could be incorporated into the main games of the series, or by issuing the songs as downloadable content.