Call of Duty: Modern Warfare 2
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, 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. Among these is the ability to receive a supply drop after achieving four kills in a row, guide a Predator missile strike after five kills, and control an AC-130 gunship, or Chopper Gunner, after eleven kills. Some killstreak rewards earn kills that go towards your killstreak. For example, Harrier Strike (7 killstreak) will stay and shoot down enemies after it has bombed a general area. Players can also gain a tactical nuke if they obtain a 25 kill streak. The nuke will achieve victory in a match for the player or team that called in the nuke regardless of whether the team was winning or losing at the time the nuke was called in. Another new feature is the in-game host migration; if a match host leaves the game, or if the host struggles to support the game, a 'host migration delay' allows a new host to be selected and the game to continue. There is also the addition of an optional third person mode which can be used in certain game types.
In the Xbox 360 version of the game, the party chat system is disabled while the player is playing online in certain playlist types. This decision, designed to promote cooperation amongst team members, has caused some controversy within the Xbox Live community. The offline (splitscreen and LAN) multiplayer mode retains the experience and rewards system found online, a first for the series since the system was introduced. However, the rewards are separate from those that are earned while playing online.
For the PC version, Infinity Ward decided to implement a new matchmaking service called IWNET, which works through Steam and therefore requires Steam client and account. This system is nearly identical to the console version of IWNET. Dedicated server support is removed, eliminating the ability for mods or user-created maps to be incorporated. This removal has created anger among many PC gamers. Since the multiplayer aspect runs within Steamworks, the PunkBuster anti-cheat system utilized in previous titles has been replaced by Valve Anti-Cheat. In addition, the PC version shares the same 18-player cap as the console versions (matches are a maximum of 9 versus 9).