I quite like the relationship between the chief and cortana. It's a pretty standard game love-interest thing, but between a gentically engineered cyborg supersoldier an a true AI, which makes it interesting- though you don't really see it until halo 3. Some of the dialogue the have is pretty fun as well-'So, what's the plan' 'Well, I was going to shoot my way out' 'You look nice' 'Thank you'*slightly awkwardly*. I mean, c'mon- a 1.5 ton supersoldier being awkward towards a girl- rather amusing. Though I personally could not relate to this very much, so my observation is purely speculative- read into that what you will.
I now apoligise for this being crap, I kinda lost my train of thought. I think it ended up in Manchester.
I can feel my testicles shrink as I write this. Oh well, ho-hum, it's not like i'm using them a lot. And you know what, I don't really care.