Modern Warfare 3's campaign should take you roughly 4-7 hours to complete. This is based on our run through the single-player component on Regular difficulty, as well as on community sentiment and reports. Stealthier runs that take time to explore the open missions can make the completion time vary drastically.
Call of Duty: Modern Warfare 2 has three different game modes: Campaign, Spec Ops, and Multiplayer. Campaign is a single-player mode where the player completes eighteen levels connected by an overarching plot.