New Vegas' treatment of sexuality has been the source of some controversy and a lot of praise. Feminist/LGBT gaming site Border House has a guest editorial praising New Vegas specifically for picking asexuality as the default and letting the player pick their preference.
I hold a lot of respect for New Vegas' approach to the PC's sexuality, in which the game specifically responds to the PC's expression of his or her sexual orientation. The PC's orientation is embedded in the text of the game, which makes everything feel more interactive and personalised to the PC's preferences.
To demonstrate, let's look at the following paraphrased chat with Zevran of Dragon Age: Origins:
Zevran: (My sexual history is varied. I . um, like banging dudes. Does that offend you?)
Grey Warden: (That's fine I don't mind.) Or: (Are you kidding?) Or: (Am I supposed to be offended?)
At no point can you say, as a man, (Oh, me too!) or as a woman, (Oh, thanks for the offer, but I like women.) Or even, (Of course I don't have a problem with your bisexuality I'm bisexual, too.)
In Fallout: New Vegas during a conversation with Cass about the harsh life of the Mojave, she says: (I'm not one for soft living . or soft men, let me tell you. I'm guessing neither are you.)
Depending on your perks, there are diverse conversation options available in which, variously, you can flirt with Cass, chat about her bisexuality, or snigger with her about erections. It all feels much more personalized and focused on the PC's orientation and characterisation. Also, erection jokes. Win-win!