Call of Duty: Modern Warfare 2 for PC features:

• Epic single-player campaign: The epic single-player campaign picks up immediately following the thrilling events of Call of Duty 4: Modern Warfare.
  
  
• Special Ops cooperative: Enjoy an entirely new gameplay mode supporting two-player cooperative play via online or split screen, unique from the single-player story campaign. Special Ops pits players into a gauntlet of time trial and objective-based missions. Rank up as you unlock new Special Ops missions, each progressively more difficult. Missions include highlights from the single-player campaign, fan favorites from Call of Duty 4: Modern Warfare, and all-new, exclusive missions.
  
  
• Multiplayer reinvented: Setting a new bar for online multiplayer, Modern Warfare 2 multiplayer delivers new enhancements including customizable killstreaks, accolades (post-match reports), an an evolved Create-A-Class system including new equipment, secondary weapons, riot shields, perk upgrades, and bling (dual attachments).