The player assumes the role of various characters during the single-player campaign, changing perspectives throughout the progression of the story.
Each level is a mission that features a series of objectives that are displayed on the head-up display, which marks the direction and distance towards and from such objectives. Damage to the player is shown by blood appearing on the screen. The player's health regenerates as time passes. Tasks vary in their requirements, from having the player arrive at a particular checkpoint, to eliminating all enemies in a specified location, to defending an objective from enemy attack, or planting explosive charges on an enemy installation. The player is accompanied by friendly troops who cannot be issued orders. Laptop computers that contain enemy intelligence appear throughout the campaign and may be collected.
Call of Duty: Modern Warfare 2 features a cooperative mode titled Special Ops, which consists of independent missions similar in design to the "Mile High Club" epilogue mission from Call of Duty 4. These missions take place in a variety of locations from the campaign mode, but are not related to the campaign. Most of the Special Ops missions may be played alone (except 2 missions, which require two players, both missions in the "Bravo" group), but all missions support two player cooperative play in which two players can play together locally or online. Scenarios included are a snowmobile race between the two players, one player providing air support from an AC-130 with the other player conducts operations on the ground, capturing an enemy compound, and searching areas for and eliminating 40 or more enemies at a time.
Special Ops is divided into five separate groups of missions: Alpha, Bravo, Charlie, Delta, and Echo. Each mission may be played at three difficulty levels: regular, hardened, or veteran. Successfully completing a mission earns the players stars, with up to three stars available for each mission; one star for completing the mission on regular difficulty, two for hardened, and three for veteran. Once enough stars are earned, more missions are unlocked. There are a total of 23 missions with their respective 69 stars available for unlock. At the end of each mission, a statistics screen displays how long the player or players took to complete the level and how many kills were scored by each player, amongst other data.
The online multiplayer mode of Modern Warfare 2 retains the same experience points and unlockable reward system as that of Call of Duty 4, with game modes that include Free-For-All, Search & Destroy, Demolition, Sabotage, Domination, Team Deathmatch, Mercenary Team Deathmatch, Headquarters, and Capture The Flag. Modern Warfare 2 introduces several new features. Aside from new weapons, equipment, and perks that upgrade to "pro versions" after meeting utilization requirements,[ the player can choose three of fifteen killstreaks, which are earned after getting a certain amount of consecutive kills without dying. Among these is the ability to receive a supply drop after achieving four kills in a row (along with the other killstreaks).