Honestly, Cortana isn't losing any of her "Cortana-ness", for lack of a better word. She is still going to have great banter with the Chief, and all of her complexities and flaws that have been developed in the previous games will become if anything, more evident than they have been in the past. To me the added sex appeal of Cortana almost completes her; if she were an actual woman she would be entirely desirable... extremely intelligent, witty, compassionate, perhaps even brave. It only seems natural in my mind to have such a desirable persona take on an equally desirable form for its physical manifestation.