Bungie’s David Dague has gone on record to describe the studio moving on from Halo to Destiny as liberating.
Dague explains further that Bungie always conceived of the original Halo: Combat Evolved as a game that could stand on its own. The succession of sequels and remakes were a happy result of an unexpected unprecedented success. Dague did not mention it here, but perhaps Bungie had more modest expectations when they initially released Halo coming from Marathon.
Dague also points out that many people in Bungie wanted to move on from Halo, and that they did not really lay down plans on how Halo’s sequels came out. In comparison to Marathon, which saw one game a year for three years, with comparatively little changed technology, Halo received palpable technical as well as gameplay upgrades with every Halo release. Bungie ended up releasing five Halo games in the span of ten years.
Destiny’s development represents an entirely new experiment for Bungie. They laid down the infrastructure for a game that will not receive sequels or spin-offs, like either Halo or Marathon, but will receive new content for the following ten years. Bungie faces the challenge of keeping fans engaged and interested with Destiny in the next decade, and it is one they have accepted in advance.