The Paramount+ Halo series has been released for some time, and fans have noted some of the many ways it has departed from the game's lore. The show has been stated to take place in the "silver timeline," according to Halopedia on Twitter, which allows the show to make its own decisions with regard to character arcs and story beats.
While some fans might take issue with the changes being made, it's fair to say that the series is in a different medium and would need some different structure. This applies just as well to the many canon Halo novels, most of which took liberty with the Halo game universe by utilizing different characters, settings, and exploring the lore.
Halo: Glasslands
This is perhaps the most recommended novel in the Halo universe and provides not only more backstory on the political situation among the UNSC and Earth as a whole, but it also gives more exploration of important backstory. Glasslands also gives more information about Halsey, the doctor behind the Spartan program.
But perhaps more core to this novel is the way that it explores the Spartans who face off with the far more advanced Covenant forces in one of the best-known missions in the series. This novel also shows the horrors of the titular glasslands - outer worlds which were 'glassed' by covenant attacks and all but wiped off the map.
Halo: The Fall Of Reach
The Fall of Reach is one of the earliest Halo novels and, as such, is a good piece of the franchise's history. It is written as a prequel to the Combat Evolved video game and gives a straightforward history of John-117's history, including how he came to have his iconic armor and his first meeting with the AI Cortana.
Unlike most other novels, this one doesn't dwell for very long on the brutal indoctrination and experimentation that young John-1117 goes through during the Spartan program. This novel is one of the easiest to read, providing fans with an easy point of entry into the novels as a whole - without a lot of in-depth consideration of the universe's implications.
Halo: Cryptum
This is the first book in a three-part trilogy, but it's easily one of the best lore-focused pieces of Halo fiction. This trilogy explores the early days of the Halo universe and provides more information on the forerunners - hence "The Forerunner Saga." But fans should be warned that this trilogy isn't for the more casual reader.
This trilogy trends towards density, spending a good deal of its space on exploring the society of the forerunners and how they lived. But once the plot points get started, readers are given the long and sad tale of Bornstellar-Makes-Eternal-Lasting and his exploration of Earth ages before the plot of Halo: Combat Evolved.
Halo: The Thursday War
In this follow-up to the Glasslands novel, the story picks up right where the previous entry left off. Without spoiling too much, this novel focuses on the burgeoning civil wars of the Sangheili and human societies, with the story of the black-ops Spartan team trying to get one of their own out before war breaks out.
This follow-up builds on the societal issues that impact both societies and gives a relatively even-handed examination of both. The overt militarism of the Halo series often becomes very black-or-white, and the willingness of some of these novels to explore the Covenant from a more generous perspective is refreshing.
Halo: Renegades
This novel is actually a follow-up to the shorter novella Halo: Smoke and Shadow, but this sequel stands on its own very well. The general storyline follows the crew of the scavenger ship, the Ace of Spades. In the course of an incredibly hard salvage mission into a forerunner debris field, the crew finds themselves caught between the UNSC and the Covenant alike.
The story of Renegades is unique in how it explores life among humans who aren't in or around the military in the 26th century. The complicated nature of day-to-day life in the midst of a galactic war comes through in the quiet moments between the chaos the crew finds themselves thrown into.
Halo: Oblivion
In another novel focused on Master Chief's story, giving him a voice and more to quote, Oblivion supplies a bit more of the adventuring experience that players of the games might want more of. This novel is focused on John and his team's attempt to take control of a disabled Covenant frigate, which is filled with valuable technology.
Of course, this turns out to be a trap, and the Spartans must fight their way through waves of Covenant forces, explore a harsh and unforgiving planet, and keep themselves alive. The novel is slightly better at exploring the universe than the previous book, Silent Storm, but it remains an easy introduction to the novels via a John-117-focused story.
Halo: Primordium
In the sequel to Cryptum, Primordium continues to follow the long-forgotten history of the Halo universe. Told via flashbacks of the forerunner AI 343 Guilty Spark, readers are told the long-forgotten history of humanity as it was when the forerunners were still around. This human perspective helps ground the story that focuses on ancient aliens and epic universe-shattering weapons.
As another entry in the Forerunner Saga, this novel gives readers a lot to digest, particularly around the deeper lore of the series, such as things like the "Mantle of Responsibility," which is the responsibility for other species that the forerunners believe was given to them by an even older and more advanced race.
Halo: Evolutions
Soren-066 is one of the main characters in the Halo television series, a defector from the Spartan program. After experiencing significant physical effects from the process of becoming a Spartan, he was disqualified and sent on his way. Evolutions is a collection of short stories that includes much of Soren's story.
This novel is likely of most interest to fans who have seen the show due to Soren's appearance as John's 'old friend.' Their relationship continues to develop on the show, but fans will be able to read more about the intricate and difficult backstory in the collection - as well as other short stories that build on similar characters.
Halo: Mortal Dictata
In the final entry of the Kilo-Five Trilogy, Mortal Dictata follows up on Glasslands and the Thursday War by bringing the Spartan group home after the end of the Covenant war. This novel is focused on the boiled-over tensions of human society that have been released by the end of endless war and the military violations that tore families apart.
The Spartan program that created John-117 and the others has a long history of ethical and moral violations that are intended, on some level, to show what humanity is willing to do for hope in a war against an unbeatable enemy. But this novel shows the exact horrors and pain that the surviving family goes through and questions its necessity.
Halo: Silentium
In the last novel of the Forerunner Saga, readers are given an exploration of the forerunners and precursors in their last days of power before the Halo weapons are activated for the first time. The novel returns to following Bornstellar-Makes-Eternal-Lasting and Catalog, a forerunner investigator.
Catalog is gathering information about the last battle at the forerunner capital and what happened, and the reader is provided with more and more information about the Didact, the flood, and a better understanding of the universe as it was long before the UNSC and John-117 came into the picture.