The biggest difference is in terms of the game focus. Declassified is not about the big campaign storyline and huge cinematics, it’s more focused on the multiplayer essence of Call of Duty and bringing that to a portable device as completely as possible, and in bringing short, objective-based missions and score-driven gameplay with lighter story elements to create what we call the Operations missions.
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I have no faith in this anymore. First the lack of a zombie mode now a focus on the multiplayer aspect.