First, one thing that has been haunting me for EVER: I know this doesn't sound serious to you, but I am honestly really disturbed by the terminal on Blaspheme Quarantine where Durandal says "'cause I got a shotgun, and you ain't got one" because THAT IS NOT PROPER GRAMMAR if it's the answer to the question "what is my purpose in this universe?"
Argh it feels painful just to look at it =)
Well, the real thing I want to say is, did you notice that Durandal goes through a huge personality change during marathon 1? The first thing you hear from him is "You've been kidnapped, do what I say or die!" "If things aren't working it's because I'm laughing so hard" and he feels scary and psychotic in every way possible.
But after a few levels, and especially in M2, he treats you like his best friend and acts more like Leela in the first levels of M1. Don't tell me that he's gone to another stage of rampancy because this doesn't fit in... Maybe Bungie made him nicer because they thought it would be irritating to play a whole game with an AI that just keeps mocking you =)