As far as labeling, I believe the standard "this is a m/m game with explicit scenes" is fine for most games. The only time a game should include a more detailed list if it goes beyond "normal" sexual encounters (water sports, bondage, humiliation, etc).
As far as my preferences, who tops or bottoms doesn't matter as long as the story is good. I prefer a game with great story and great smut. But a game that heavily focuses on sex, I think it matters a lot more who tops/bottoms.