Bungie is very good at not overly sexualizing their female characters. Even Cortana, who takes the form of a completely unclad woman, never felt like a sad attempt at eye candy, to me, at least. If you play Reach, you'll see that female Spartans look as soldierly and professionally as the males. Take a look at the Titan concept art and the "Law of the Jungle" trailer. The Titan is a woman.