I will agree that LGBT characters aren't very well characterised in games, but at the same time, it's also worth pointing out that while some LGBT characters in games do have an explicit reference to their orientation, sometimes leaving things up to interpretation is also good, at least at the moment. I've got three examples off the top of my head at the moment. Lara Croft from the recent Tomb Raider was written ambiguously, and so was the main character in Assassins Creed Liberation. Persona 4 kinda made things more ambiguous in the English translation compared to the original Japanese.
It might be best to take a look at instead at games where sexuality is more important in order to figure out how well represented LGTB characters are, so if there are romantic subplots, or parts of the story where characters are coming to terms with their identity, then that'd be a very relevant place to place and examine whether LGTB themes or character are present, and how it's represented.
I also understand that there's support for casting things like they did in Aliens, but at the same time, while a sexuality isn't part of a personality, it can be part of someone's identity, which can inform how they relate to others depending on situations, just as much as nationality and gender are facets of identity and should act as such. So yeah, that's my two cents.