By the power of truth, I, while living, have conquered the universe.
Ah, the agony of choice.
I'm stuck between the Truth and Reconciliation, 343 Guilty Spark and the Maw.
T&R was fantastic in literally every way, it was atmospheric and ambient with great combat scenarios (grav lift fight on Legendary still gives me shivers when the Hunters drop down) and Under Cover of Night is an utterly divine track. How does the mission end? Keyes rams a group of Hunters with a Spirit, that's too badass!
343 Guilty Spark was another unique level. It's full of tension, like T&R it's ambient and has some very atmospheric music. The scene where the Flood is introduced was amazing too, it was a mission that genuinely scared the living -blam!- out of me whenever I played it during the night with surround sound.
The Maw was such an epic conclusion to the game, especially the infamous Warthog Run through the Autumn whilst everything is blowing up. I had a wild-cat destabilisation in the excitement department when John said that it was just the beginning, then seeing 343 drifting through space - after I worked so hard to kill that bastard.