Some may be wondering why Bungie felt a need to break away from Microsoft if they seem content working on the Halo series for all of eternity. According to Bungie's GDC panel, the team is currently working on a number of projects, something Bungie never had the capacity to do. Since then, the team has expanded considerably, allowing Bungie to pursue non-Halo projects.
Bungie's growth seems to parallel the path of another acclaimed FPS developer: Valve. Perhaps Halo can follow Half-Life's footsteps: expanding episodically, whilst introducing innovative concepts like Portal.