Halo: Fall of Reach was put out originally as a novel before Halo: Combat Evolved launched with the original Xbox. It was a good read and did a good job of setting up the back story. Now it is being adapted into comic book form.
The Halo universe has built up a sizeable back story through not just the Xbox 360 games but also through other media such as books, comics, and animated films. Now Marvel Comics and 343 Industries are producing a new comic book is coming out this September that graphically depicts the events in the Halo: Fall of Reach novel.