Here is an interesting comparison of Cortana over the course of the 4 halo games:
PTesh adds his dulcet prepubescent tones over the top of one of the new trailers for weapons...
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Level: The Maw
If you finish "The Maw" on Legendary you will see a bonus cut scene that shows the Pillar of Autumn blowing up with Johnson and an Elite hugging because they both know they will die. The cut scene is interesting in the fact that it's later referenced by "Guns" in Halo 2 when he asks "When are you going to tell me how you got off that ring?" to which Johnson replies, "Sorry Guns, that's classified".