The movie can't deny it's video-game origin, especially the main protagonist never comes alive. But it is filled with endless action and suspense to make up for this.
What's it about?
After a fierce space-battle, the Master Chief crash-lands on the ring-world of Halo and while he struggles to stay alive, he slowly reveals the true nature of the mysterious object.
The 'Pillars of Autumn', jumps through space to escape the ships of the Covenants. By accident it comes out near Halo, a huge ring-world with it's own atmosphere and gravity. The lone ship stands no chance against the opponent fleet and Captain Keyes orders the Master Chief, a genetically altered super-soldier to take the ships AI down to Halo and protect it. He crashes on the surface, as does the 'Pillars of Autumn'. The Master Chief encounters a few other survivors and together they build a base camp.
The survivors find out, that Captain Keyes was taken hostage and the team decides to rescue him. They go aboard the Covenant-ship, that is docked along the ring-world. They manage to get out of the ship alive with the Captain and it is revealed, that Halo was constructed by the "Forerunner", an ancient alien race, and that it can be used as a weapon. To find out more about Halo, the Master Chief heads towards the subterranean Map Room, while Captain Keyes goes to the crashsite of the 'Pillars of Autumn'. After some heavy fighting at a beach, the Master Chief reaches the Map Room, where the ship's AI is seemingly destroyed trying to connect to the Map Room's computer. Now the Master Chief doesn't know where to go, when suddenly he is attacked by Flood Infections, which can infect all the human soldiers and turn them into infected zombies.
The Master Chief is running out of ammo and it looks really grim, when suddenly Guilty Spark appears. It is a floating robotic device shooting down the whole army and asking the Master Chief to follow him to the Command Center of Halo. More than gladly he follows.
After battling the next Flood Army, the Master Chief reaches the inner sanctum of the Command Center and is asked to start the Sterilization Sequence to stop the Flood Infection. Fittingly in this moment the ship's AI re-awakens and stops the activation, as this would have killed every human in the galaxy. The Master Chief shoots and Guilty Spark and flees.
The only way to stop the Flood Infection from spreading throughout the universe, is to destroy Halo, by over-charging the energy core of the 'Pillars of Autumn'. He fights his way through the crashed ship and encounters in best final boss style the infected Captain Keyes. After killing him, the Master Chief activates the over-charging sequence and can flee from Halo on the last ship left. From afar he watches the ring-world explode and with it the menace of the Flood Infections.
Computer Game Structure:
I wrote a post about the Quest Structure of 'Clash of the Titans', and most of it applies here, too. There is no overall story goal, there are small level-like mini-goals and neither the protagonist nor the viewers know where the story wants to go. It makes such a epic movie feel small. Master Chief, the leader of the Spartans, has to go from the Covenant-ship to the Map Room to the Command Center to the crashed space-ship. These are not the steps of the Hero's Journey, these are recreations of the game's different stages. As such it is never-ending action from the first page to the last. But the set-pieces are amazing and the shoot-outs thrilling...
The Master Chief is a genetically altered super soldier, he doesn't speak much throughout the movie, nor shows any deep feelings. We see his face only once in a dream sequence and for the rest of the film he wears his suit and helmet. His companion, the ship's AI, is even less alive. She talks in his head and gives directions. There is not a single scene describing the motivation for the Covenant wanting to kill every human; Guilty Spark is a robot and as such also very much away from being a identifiable character. The last antagonist, the Flood Infections, are just a zombifying flesh-eating alien virus, so not much persona there. As you see, the whole movie is void of human characters, of emotions, of motivations or anything resembling it. Most probably it is a faithful recreation of the game, but I doubt it would work in a movie.
The 'Halo' Series, produced by Bungie and Microsoft, sold over 40 million copies, worth 2 billion dollar worth of revenue, since 2001. Four years later the movie adaptation started with Alex Garland writing this draft of the Halo script. 20th Century Fox and Universal Studios partnered to produce the film. Peter Jackson was set to produce with Guillermo del Toro first, then Neill Bloomkamp directing. 2006 D.B. Weiss and Josh Olson revised the script, but the project fell apart soon after that. The rights to make the reverted back to Microsoft, who promises to make the movie sometime in the future.