In short, the voice is an evil entity 'playing' with Kevin and Kaylee. Kaylee doesn't play by its arbitrary rules and is removed. The repeating cartoon disappearance shows exactly what the entity is doing to Kevin, tormenting and mutilating him over and over again for its own amusement, for 572 days and into infinity.
Modern Warfare takes place in modern time, with the campaign occurring over the course of several days in late 2024, and the Special Ops and multiplayer modes continuing the story into 2024.
The Modern Warfare III Campaign features four difficulty levels. The higher the difficulty level, the greater the challenge. Note that you can change the game's difficulty level at any time. Recruit: For players who are new to Call of Duty.