The Halo universe is large and interesting, but it you only look at the stories in the games it is all pretty confusing. That is why Microsoft and Bungie have teamed up with sci-fi author Eric Nylund on a series of books that help to flesh out the universe and connect everything so it makes sense. The three books The Fall of Reach, The Flood, and First Strike are fun to read and make you appreciate just how great the Halo games and overall universe really are.
The Fall of Reach
The first book in the series is called The Fall of Reach. The Fall of Reach details the origins of the Spartan program and also covers the beginning of the war with the Covenant leading all the way up to the discovery of the first Halo. I particularly like the parts of the book that deal with the training and special abilities of the Spartans and their place as the best soldiers in the human military. Master Chief isnt the only Spartan, by the way. If you have ever read Robert A. Heinleins Starship Troopers, The Fall of Reach is told in a very similar manner which is a good thing. The title, The Fall of Reach, references a human controlled world called Reach that is a major staging area for the military. The Covenant discover the location of Reach and the resulting chaos leads to a random slipspace (basically hyperspace or light speed in other sci-fi universes) jump where Captain Keys, Master Chief, and the rest of the crew of the ship Pillar of Autumn discover Halo.
The second book of the series is called The Flood and is basically a novelization of the first Halo videogame. Pretty much every memorable part from the game is recreated in the book exactly the same way you remember it. This method of storytelling is sort of disappointing since we have literally done all of this before, but it is interesting at the same time because it does a good job of detailing the threat that Elites and Hunters pose as well as the horrible destructive nature of the Flood that cant really be conveyed in the game. The book also makes a nod towards Halo 2 by telling the story from the perspective of both the humans and the Covenant on Halo. This book is the weak point of the three Halo books since it doesnt really cover anything new, but it is still a fun read.
The last book of the series is titled First Strike and follows Master Chief and a handful of other survivors as they try to get back to Earth and warn them about the Flood. The group is able to capture a Covenant ship and on a hunch they head back to Reach to search for any survivors. What they find is a group of Spartans and a crystal that warps slipspace and also happens to be a holy relic of the Covenant. They also discover the horrible news that the Covenants next stop on their galactic tour looking for holy relics is the Sol system, i.e. Earth. They learn that the Covenant fleet is massing at a huge space station before they make the jump to Earth, so Master Chief leads a team of Spartans to destroy the station and as many Covenant ships as they can. The mission is a success, but the hundreds of ships destroyed were only a small part of the Covenant fleet so the group races back to Earth and that is where Halo 2 begins.
All in all, the three Halo books are interesting to read and give you a much greater understanding and appreciation of the overall Halo universe. With all of this backstory filling in the gaps left by the games, Im actually fairly confident about the future of the Halo series. As strange as a lot of Halo 2 was, there is reasoning behind everything and all will be revealed down the road in Halo 3 or the rumored Halo movie or perhaps even more books. This is a franchise that has a solid foothold in not only videogames but also science fiction and it isnt going to go away any time soon. Reading the books will make you appreciate Halo and Halo 2 a hundred times more, so I highly recommend them.
You can purchase the three books in a box set for under $15 in most bookstores.