Humanity has paid a heavy price for their battle against the deadly Covenant at the ancient ring world known as Halo, but destroyed it before its power wiped out the galaxy's sentient life. And SPARTAN-117, the Master Chief, must return to Earth with the information on the recent discovery. However, he comes upon another creation left behind by the mysterious Forerunners, and it may be up to him to save the last of his Spartans, along with the human race, once again, from the Covenant and their desire to find the artefact...
The game is based on the novel Halo: First Strike, by Eric Nylund. It is played mostly in first person, and will often vary between characters. The mission may also be altered if played cooperatively.
The campaign consists of 14 levels, 13 of which are part of the storyline and 12 of which are playable:
Like Halo 3: ODST, Halo: First Strike alternates as the player character. Player 2 also varies between a different character and a double of player 1. Most missions are played as one of the UNSC Spartans, although there are some that feature playing as a Marine. On specific levels or parts of levels, the player can choose which "class" of soldier they want to use (three classes, two soldiers of each class, one of each gender), and will receive the corresponding weapons and equipment.
While the HUD differs, the experience of playing as a Marine is similar to that of ODST, with stamina and health limit. MJOLNIR Mark V armour is also used by the Spartans, which renders them to a health display. However, the player always has a medical kit which includes 3 canisters of biofoam that can be used at any time during the game. Health packs are also located in various parts of the level, although they are more scarce than in Halo: Combat Evolved or Halo 3: ODST.
New navigation methods are also added, such as the tactical map (or tacmap for short), which can be used for giving orders to AI teammates, and allowing the player to explore in the open environment levels without getting lost. Some parts of missions may also allow the player to move only inside a vehicle.
In addition to new weapons, existing ones from previous Halo games are featured, with some balanced modifications. The player can change the rate of fire to their preferred mode. Firefight also contains new characters, maps, and additional features.
Firefight features 10 playable maps, and can be played as six different players. The rules are similar to that of Halo 3: ODST, with 4 players maximum locally or online. However, AI teammates can also be featured, with no ties to life limit and can be turned on or off. When chosen, AIs can be toggled in quantity for a maximum of 5 total Spartans. For example, when playing in single player, there can be 0, 1, 2, 3, or 4 teammates. When playing 4-player cooperative, only 1 AI can be turned on or off. Each Spartan can have their helmet removed, with the exception of John-117.