Music plays a large part in my games, always has. I've talked a little bit of heavy metal and it's influence in my fantasy gaming, but my science fiction games have tended towards a more synthetic sound. Balancing music and voice is a difficult proposition when you have several people talking, usually at different volumes and the details are important. So I tend towards more ambient sounds and unobtrusive themes for science fiction. One of the best soundtracks I have ever had was for the game Mechwarrior 2. Check this sample out. It perfectly balances an evocative sound, science fiction sound effects and themes, 90's era action movie feel and unobtrusiveness.