The core rationship between Cortana and Mister Chief was pretty good...

Just a shame that A, the game suffered for it narratively (By introducing an unwanted antagonist, and just focused on MC and Cortana.) and B, I would have felt something for it if Master Chief had a glimmer of a personality, or at the very some way to emphasize with him (it's hard to feel anything for MC, since he's a faceless largely voiceless killing machine).