The only thing that bugs me about is that it makes the NPCs in mass effect, a series praised for it's writing, nothing more than wish fulfillment vessels to the player.
This is a tricky situation because video games are supposed to either be empowered or in control of their world. But, as an example, I actually didn't know you could sleep with Ashley in ME1 and I thought it was because of her religious convictions. This didn't bug me, it earned Bioware kudos from me for writing a good and believable character (I didn't sleep with anyone because Liara wasn't my type).
Now Jacob has had a relationship with Miranda, it's brought up early on in ME2. I never got any gay vibes of Jacob in ME2. But if the player wills it, he can make Jacob gay. If the player doesn't go down the gay route in ME3 Jacob will be heterosexual, if the player goes down the gay route in ME3 Jacob will be homosexual.
This might sound stupid but it bugs me that NPCs are not being written as characters with their own motives, beliefs, etc. and instead are around simply to adapt to what the player wants out of them. I think overall that makes a less compelling story, although a much more compelling power fantasy fulfillment simulator.
How many people do you know who would honestly switch their sexuality at the drop of the hat? or go both ways? I know bi-sexuals exist, but almost everyone in a Bioware game seems to be that way and I think the bi-sexual example is being used as a cover for what I view as poor character development.
I would prefer some more concrete sexuality. Some characters that are purely gay, purely homosexual and then some benders. I think it would ultimately lead to stronger characters as their motives are based on their wants instead of mine (as the player).