I'd like to see an actual relationship. ME1 made sense, but ME2 really crapped its pants on this one, I think. Shoehorning non-Liara LI's out of the plot (and, hell, even her without that DLC) and trying to get you to go through the same old motions as in ME1 is just, well, dull. If you didn't romance anybody in ME1, sure, I can dig it. But why throw away that stuff in ME2 in such a generic handwave? I thought an epic trilogy like this would take a pre-existing relationship in an interesting direction.
That's just one of the many things ME2 dropped the ball on, I guess. But it's one of the main things I wanna see remedied, as well. If people stick with Ashley or Kaiden or Liara, let's see that in ME3 from the beginning. Not a rehashing of the ol' "be nice to them at ALL TIMES, flirt vaguely, then bang before the final suicide-ish mission". A real, existing relationship from start to finish (maybe one that can hit rocky patches and the like, who knows) is interesting stuff.
Sex scene? Eh, I'm not bothered by that. But yeah, ME2 was pretty tame. Hell, ME1 was kind of tame, really. But yeah, BW should go balls out on it and just do whatever feels right for the characters. To hell with Fox News evangelists and lunatics. But I'm more interested in seeing a relationship that already exists try to survive the apocalypse. I guess that'd mean you could have do stuff with 'em (drinking, sexy times, whatever) multiple times over the course of the game, and that'd be neat.