Halo Primordium

Halo: Primordium is the second book in The Forerunner Saga, a trilogy of Halo Expanded Universe novels by Greg Bear. The book takes place during the time of the Forerunners, the ancient race that built the Halo rings encountered in the games. Though mostly set during the Forerunners' war with the Flood, the novel is told as a series of logs narrated by a Forerunner Monitor discovered by an ONI science team. The monitor explains that it was once a human named Chakas (one of the main characters of the previous novel Halo Cryptum) and proceeds to tell its story, which turns out to involve a lot of walking around on a Halo.

Tropes used in Halo Primordium include:

Abusive Precursors: Though foreshadowed in Cryptum, Primordium reveals that The Precursors created various species and would occasionally annihilate them at will. They were about to do this to the Forerunners, but they struck first and destroyed the Precursors instead. Despite this, the Precursors managed to leave the Flood behind to eventually exact their vengeance on the Forerunners.
Big Damn Heroes: The Forerunner fleet led by the Didact arriving to retrieve the Halo before it smashes itself on the wolf-face planet.
Brain Uploading: How Chakas eventually became 343 Guilty Spark.
Deadpan Snarker: The Lord of Admirals.
Enemy Civil War: Sorta. The Forerunners are fighting each other more than they fight the Flood (at least, on the one Halo); the Builders under Faber claim authority and abuse their power, while many Lifeworkers and Warrior-Servants still serve the Librarian and resist them.
Hope Spot: When they find the human village run by Genemender. It looks like they've finally found somewhere safe... but then it turns out everyone there is dead, the visions they're seeing simply holograms of their AI walking around. Then the power shuts down, Gamelpar dies, and they have to move on.
I Know Your True Name: Spoken verbatim by the Didact when he arrives at Installation 07 and uses Mendicant Bias' "true name" as a shutdown code. Curiously, the same name worked only momentarily in Cryptum.
The Obi-Wan: Gamelpar to Chakas.
The Reveal: As revealed by the Captive, the Flood was engineered by the Precursors as a test to judge a species' worthiness of the Mantle, and there never was a cure to the Flood, as many had believed until that point).
Weird Moon: The wolf-face planet that keeps growing closer. Turns out the Halo is trying to self-destruct by smashing itself on it.
Worthy Opponent: How the Didact and the Lord of Admirals viewed one another.