Source: Wikipedia
Set in 2019, you play as Jake Dunn, a United States Delta Force operator. Dunn and his team are sent to pacify a situation in which a group of United States archaeologists are taken captive by the North Korean military while investigating a mysterious ancient artifact that was found in the Spratly Islands, located in the South China Sea.
As the story unfolds, players are faced with three very different environments (or "acts"):
Act 1: An ancient artifact on the islands begins to show signs of activity, causing the North Koreans to take up military presence and investigate the artifact site. As a Delta Force soldier, you HALO jump onto the island to see what you can find out for the US Government. During this phase of the game, you'll play in a tropical environment complete with beaches, jungles and tropical villages.
Act 2: The meteor opens up and flash freezes a large part of the island. There is no clear alien threat, however, so both parties continue to fight each other. The player's main objective is now to investigate what's happening on the interior of this frozen sphere. Shortly after, both the North Korean and US governments come to the realization that this meteor is actually an alien craft, and therefore decide to join forces to fight what could become an alien invasion. This phase consists of battling through the frozen jungle as well as on your own aircraft carriers, which are located off the coast. The aliens, not yet revealed in the story, use machines to battle against the North Korean and US militaries, which are slowly closing in on the source of the freezing – an alien ship lodged in the earth's surface. The constantly expanding freezing sphere throws the global weather system off balance and causes natural disasters which include high winds, tornadoes, and earthquakes.
Act 3: As you enter the alien craft, you find yourself not only weightless, but fighting against the aliens in this gravity-resistant environment. The recoil of weapons combined with the Zero-G environment propels players back while leaving shell casings from weapons floating beside you. The Zero-G portion of the game will only last about 1 hour, however. Crytek has stated the aliens themselves will not be revealed until this part of the game, giving them a certain degree of suspense.