Although episodic game development makes all the sense in the world theoretically, things seem to get problematic in practice. The SiN: Episodes series turned out to be poorly named, given that Ritual Entertainment managed to release only a single episode before suspending the project and
being acquired by casual-game publisher MumboJumbo. Meanwhile, Valve's episodic treatment of Half-Life has been well-received, but annualized franchises were able to launch multiple full-fledged sequels in the 16-month gap between the first two Half-Life episodes.
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Source: Gamespot