1. Truth and Reconciliation: Belly of the Beast at the top of the gravity lift. Overwhelming waves of enemies that actually can do damage if you don't pay attention, including camoflouged Elites and Sword Zealots. 2. Silent Cartographer: Numerous camoflouged Elites waiting in ambush after deactivating the security door. 3. Assault on the Control Room: final room completely filled with enemies, including multiple Elites and a Sword Elite. 4. The Library: Huge, HUGE mob at the end that all-out charges you, forcing you to think on your feet. 5. Two Betrayals: Final Run. Massive three-way battle between Covenant with multiple Wraiths, Hunters, and dozens of infantry, dozens of Flood with rocket launchers, and the player. 6. Keyes: Proto-Gravemind (bridge) room. Flood charge out of most doors while Covenant wait to ambush through another. Can be lured into wiping each other out, literally. 7. The Maw: Engine Room; Sentinels & Flood constantly attacking you. Plus the epic Warthog Run. Does that suffice?