Summary pulled directly from Steam - Some text may only be applicable to Steam platform

• Pulse-racing new installment from 2007's PC Game of the Year*: Play as Sergeant Sykes and experience a whole new side of the battle. A standard combat mission behind enemy lines becomes critical when you discover your enemies have captured something of vital importance to the ensuing war. It's down to you to retrieve the cargo, at any cost.
  
• More explosive and dynamic minute to minute game play: new customizable weapons, new vehicles, new photorealistic locations to explore, and a fully interactive war zone to dominate.
  
• Enhanced human and alien AI: Intelligent enemies, bigger challenges, and all-new ally squad support.
  
• Crysis Warhead is a standalone release and does not require ownership of Crysis to play.
  *PC GAMER